sharon sanders
Editor-in-Chief & President
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US FluView - Weekly Surveillance Flu report 2021/2022 season - for trend analysis
- Thread starter sharon sanders
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sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated February 4, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 4, ending January 29, 2022
Influenza activity has decreased in recent weeks, but sporadic activity continues across the country.
Viruses
Clinical Lab1.7%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.0%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 4 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.5%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.4 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations827
patients admitted to hospitals with influenza
this week.
NCHS Mortality28.6%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week, with a total of 5 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 6,378 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 361 (5.7%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 526 influenza viruses collected since October 3, 2021. Most of the H3N2 viruses so far are genetically closely related to the vaccine virus, but some viruses demonstrate antigenic differences that developed as H3N2 viruses have continued to evolve. Virus antigenic data will be reported later this season when a sufficient number of specimens have been tested.
CDC assesses susceptibility of influenza viruses to the antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 4, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Two of the 10 HHS regions (Regions 7 and 10) are above their region-specific baselines, and the remaining regions are below their baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet is trending downward for all age groups (0–4 years, 5–24 years, 25-49 years, 50–64 years, and 65+ years).
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 4, 77 (0.5%) of 14,265 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,286 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and January 29, 2022. The overall cumulative hospitalization rate is 4.4 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed for week 4 during the 2020-2021 season (0.5 per 100,000), but lower than the in-season rates observed for week 4 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 16.9 to 51.4 per 100,000 during the 2016-2017 through 2019-2020 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged ≥65 years (11.5); within this group, rates were highest among adults aged ≥85 years (24.6). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (6.2) followed by adults aged 50-64 years (4.1). When examining rates by race and ethnicity, the highest rates of hospitalization per 100,000 population were among non-Hispanic American Indian or Alaska Native persons (5.4) and non-Hispanic Black persons (5.4).
Among 1,286 hospitalizations, 1,212 (94.2%) were associated with influenza A virus, 64 (5.0%) with influenza B virus, 5 (0.4%) with influenza A virus and influenza B virus co-infection, and 5 (0.4%) with influenza virus for which the type was not determined. Among 310 hospitalizations with influenza A subtype information, 307 (99.0%) were A(H3N2) and 3 (1.0%) were A(H1N1)pdm09. Based on preliminary data, of the 1,286 laboratory-confirmed influenza-associated hospitalizations, 2.8% also tested positive for SARS-CoV-2.
Among 548 hospitalized adults with information on underlying medical conditions, 90.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 59 hospitalized children with information on underlying medical conditions, 61% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 4, 827 patients with laboratory-confirmed influenza were admitted to the hospital.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 3, 2022, 28.6% of the deaths that occurred during the week ending January 29, 2022 (week 4), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 6,050 PIC deaths reported for this week, 5,306 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 23 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 4.
A total of five influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 4, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated February 4, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 4, ending January 29, 2022
Influenza activity has decreased in recent weeks, but sporadic activity continues across the country.
Viruses
Clinical Lab1.7%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.0%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 4 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.5%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.4 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations827
patients admitted to hospitals with influenza
this week.
NCHS Mortality28.6%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week, with a total of 5 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity has decreased in recent weeks, but sporadic activity continues across the country.
- The majority of influenza viruses detected are A(H3N2). Most of the H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Some viruses show antigenic differences that developed as H3N2 viruses have continued to evolve.
- The percentage of outpatient visits due to respiratory illness decreased nationally again this week and is now below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect declined slightly again this week.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- CDC estimates that so far this season there have been at least 2.1 million flu illnesses, 21,000 hospitalizations, and 1,200 deaths from flu.
- An annual flu vaccine is the best way to protect against flu and its potentially serious complications. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccination coverage remains lower this season compared to last.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 6,378 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 361 (5.7%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 57,889 | 1,442,367 |
| No. of positive specimens (%) | 994 (1.7%) | 37,514 (2.6%) |
| Positive specimens by type | ||
| Influenza A | 964 (97.0%) | 36,644 (97.7%) |
| Influenza B | 30 (3.0%) | 870 (2.3%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 32,430 | 525,242 |
| No. of positive specimens | 398 | 10,763 |
| Positive specimens by type/subtype | ||
| Influenza A | 395 (99.2%) | 10,676 (99.2%) |
| (H1N1)pdm09 | 0 | 5 (0.1%) |
| H3N2 | 114 (100%) | 7,400 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 281 | 3,270 |
| Influenza B | 3 (0.8%) | 87 (0.8%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 1 (100%) | 33 (97.1%) |
| Lineage not performed | 2 | 53 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 526 influenza viruses collected since October 3, 2021. Most of the H3N2 viruses so far are genetically closely related to the vaccine virus, but some viruses demonstrate antigenic differences that developed as H3N2 viruses have continued to evolve. Virus antigenic data will be reported later this season when a sufficient number of specimens have been tested.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 503 | ||||
| 3C.2a1b | 503 (100%) | 1a | 1 (0.2%) | ||
| 1b | 1 (0.2%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 501 (99.6%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 20 | ||||
| V1A | 20 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (45.0%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 11 (55.0%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 527 | 3 | 504 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 527 | 3 | 504 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 527 | 3 | 504 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 520 | 3 | 497 | 20 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 4, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Two of the 10 HHS regions (Regions 7 and 10) are above their region-specific baselines, and the remaining regions are below their baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet is trending downward for all age groups (0–4 years, 5–24 years, 25-49 years, 50–64 years, and 65+ years).
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 4 (Week ending Jan. 29, 2022) | Week 3 (Week ending Jan. 22, 2022) | Week 4 (Week ending Jan. 29, 2022) | Week 3 (Week ending Jan. 22, 2022) | |
| Very High | 0 | 1 | 2 | 10 |
| High | 4 | 11 | 23 | 46 |
| Moderate | 2 | 6 | 33 | 75 |
| Low | 9 | 14 | 109 | 152 |
| Minimal | 38 | 22 | 488 | 381 |
| Insufficient Data | 2 | 1 | 274 | 265 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 4, 77 (0.5%) of 14,265 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,286 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and January 29, 2022. The overall cumulative hospitalization rate is 4.4 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed for week 4 during the 2020-2021 season (0.5 per 100,000), but lower than the in-season rates observed for week 4 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 16.9 to 51.4 per 100,000 during the 2016-2017 through 2019-2020 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged ≥65 years (11.5); within this group, rates were highest among adults aged ≥85 years (24.6). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (6.2) followed by adults aged 50-64 years (4.1). When examining rates by race and ethnicity, the highest rates of hospitalization per 100,000 population were among non-Hispanic American Indian or Alaska Native persons (5.4) and non-Hispanic Black persons (5.4).
Among 1,286 hospitalizations, 1,212 (94.2%) were associated with influenza A virus, 64 (5.0%) with influenza B virus, 5 (0.4%) with influenza A virus and influenza B virus co-infection, and 5 (0.4%) with influenza virus for which the type was not determined. Among 310 hospitalizations with influenza A subtype information, 307 (99.0%) were A(H3N2) and 3 (1.0%) were A(H1N1)pdm09. Based on preliminary data, of the 1,286 laboratory-confirmed influenza-associated hospitalizations, 2.8% also tested positive for SARS-CoV-2.
Among 548 hospitalized adults with information on underlying medical conditions, 90.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 59 hospitalized children with information on underlying medical conditions, 61% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 4, 827 patients with laboratory-confirmed influenza were admitted to the hospital.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 3, 2022, 28.6% of the deaths that occurred during the week ending January 29, 2022 (week 4), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 6,050 PIC deaths reported for this week, 5,306 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 23 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 4.
A total of five influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 4, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated February 11, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 5, ending February 5, 2022
Sporadic influenza activity continues across the country.
Viruses
Clinical Lab2.0%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.7%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 4 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.4%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.5 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations993
patients admitted to hospitals with influenza
this week.
NCHS Mortality26.3%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week, with a total of 5 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 6,774 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 402 (5.9%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 588 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve. Virus antigenic data will be reported later this season when a sufficient number of specimens have been tested.
CDC assesses susceptibility of influenza viruses to the antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 5, 1.7% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. One of the 10 HHS regions (Region 7) is above its region-specific baseline, and the remaining regions are below their baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet is trending downward for all age groups (0–4 years, 5–24 years, 25-49 years, 50–64 years, and 65+ years).
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 5, 60 (0.4%) of 14,177 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,336 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 5, 2022. The overall cumulative hospitalization rate is 4.5 per 100,000 population. This cumulative hospitalization rate is lower than the in-season rates observed for week 5 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 20.1 to 59.9 per 100,000 during the 2016-2017 through 2019-2020 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged ≥65 years (12.0); within this group, rates were highest among adults aged ≥85 years (25.4). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (6.6) followed by adults aged 50-64 years (4.2). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (5.9) followed by non-Hispanic Black persons (5.8).
Among 1,336 hospitalizations, 1,256 (94.0%) were associated with influenza A virus, 70 (5.2%) with influenza B virus, 5 (0.4%) with influenza A virus and influenza B virus co-infection, and 5 (0.4%) with influenza virus for which the type was not determined. Among 321 hospitalizations with influenza A subtype information, 318 (99.1%) were A(H3N2) and 3 (0.9%) were A(H1N1)pdm09. Based on preliminary data, of the 1,336 laboratory-confirmed influenza-associated hospitalizations, 2.8% also tested positive for SARS-CoV-2.
Among 640 hospitalized adults with information on underlying medical conditions, 90.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 68 hospitalized children with information on underlying medical conditions, 58.8% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 5, 993 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS-Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance. The increase in hospitalizations reported during week 5 may be due in part to the increase in reporting facilities.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 10, 2022, 26.3% of the deaths that occurred during the week ending February 5, 2022 (week 5), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 5,043 PIC deaths reported for this week, 4,287 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 18 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 5.
A total of five influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 11, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated February 11, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 5, ending February 5, 2022
Sporadic influenza activity continues across the country.
Viruses
Clinical Lab2.0%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.7%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 4 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.4%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.5 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations993
patients admitted to hospitals with influenza
this week.
NCHS Mortality26.3%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week, with a total of 5 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Sporadic influenza activity continues across the country.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
- The percentage of outpatient visits due to respiratory illness decreased nationally again this week and is below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect increased slightly this week.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- CDC estimates that so far this season there have been at least 2.2 million flu illnesses, 22,000 hospitalizations, and 1,300 deaths from flu.
- An annual flu vaccine is the best way to protect against flu and its potentially serious complications. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccination coverage remains lower this season compared to last.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 6,774 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 402 (5.9%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 45,382 | 1,506,399 |
| No. of positive specimens (%) | 930 (2.0%) | 38,863 (2.6%) |
| Positive specimens by type | ||
| Influenza A | 908 (97.6%) | 37,953 (97.7%) |
| Influenza B | 22 (2.4%) | 910 (2.3%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 23,242 | 582,403 |
| No. of positive specimens | 368 | 11,768 |
| Positive specimens by type/subtype | ||
| Influenza A | 366 (99.5%) | 11,673 (99.2%) |
| (H1N1)pdm09 | 0 | 5 (0.1%) |
| H3N2 | 129 (100%) | 7,905 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 237 | 3,762 |
| Influenza B | 2 (0.5%) | 95 (0.8%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 2 | 61 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 588 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve. Virus antigenic data will be reported later this season when a sufficient number of specimens have been tested.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 565 | ||||
| 3C.2a1b | 565 (100%) | 1a | 1 (0.2%) | ||
| 1b | 1 (0.2%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 563 (99.6%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 20 | ||||
| V1A | 20 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (45.0%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 11 (55.0%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 604 | 3 | 581 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 604 | 3 | 581 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 604 | 3 | 581 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 596 | 3 | 573 | 20 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 5, 1.7% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. One of the 10 HHS regions (Region 7) is above its region-specific baseline, and the remaining regions are below their baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet is trending downward for all age groups (0–4 years, 5–24 years, 25-49 years, 50–64 years, and 65+ years).
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 5 (Week ending Feb. 5, 2022) | Week 4 (Week ending Jan. 29, 2022) | Week 5 (Week ending Feb. 5, 2022) | Week 4 (Week ending Jan. 29, 2022) | |
| Very High | 0 | 0 | 2 | 4 |
| High | 0 | 4 | 6 | 22 |
| Moderate | 4 | 2 | 19 | 32 |
| Low | 4 | 10 | 63 | 105 |
| Minimal | 45 | 38 | 556 | 505 |
| Insufficient Data | 2 | 1 | 283 | 261 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 5, 60 (0.4%) of 14,177 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,336 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 5, 2022. The overall cumulative hospitalization rate is 4.5 per 100,000 population. This cumulative hospitalization rate is lower than the in-season rates observed for week 5 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 20.1 to 59.9 per 100,000 during the 2016-2017 through 2019-2020 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged ≥65 years (12.0); within this group, rates were highest among adults aged ≥85 years (25.4). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (6.6) followed by adults aged 50-64 years (4.2). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (5.9) followed by non-Hispanic Black persons (5.8).
Among 1,336 hospitalizations, 1,256 (94.0%) were associated with influenza A virus, 70 (5.2%) with influenza B virus, 5 (0.4%) with influenza A virus and influenza B virus co-infection, and 5 (0.4%) with influenza virus for which the type was not determined. Among 321 hospitalizations with influenza A subtype information, 318 (99.1%) were A(H3N2) and 3 (0.9%) were A(H1N1)pdm09. Based on preliminary data, of the 1,336 laboratory-confirmed influenza-associated hospitalizations, 2.8% also tested positive for SARS-CoV-2.
Among 640 hospitalized adults with information on underlying medical conditions, 90.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 68 hospitalized children with information on underlying medical conditions, 58.8% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 5, 993 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS-Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance. The increase in hospitalizations reported during week 5 may be due in part to the increase in reporting facilities.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 10, 2022, 26.3% of the deaths that occurred during the week ending February 5, 2022 (week 5), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 5,043 PIC deaths reported for this week, 4,287 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 18 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 5.
A total of five influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 11, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
bump this
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated February 18, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 6, ending February 12, 2022
Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
Viruses
Clinical Lab3.0%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.4%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 0 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.4%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.7 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,073
patients admitted to hospitals with influenza
this week.
NCHS Mortality22.6%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week, with a total of 5 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 7,201 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 433 (6.0%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Novel Influenza A Virus
One human infection with a novel influenza A (H1N2) variant virus was reported by California. The infection occurred in an adult ≥ 18 years of age. The patient was not hospitalized and has recovered from their illness. The patient had direct contact with swine prior to specimen collection. Respiratory illness was reported among contacts of the patient, however this occurred during a period of high respiratory illness activity and no specimens from the contacts were received for testing. No ongoing person-to-person transmission has been identified associated with this case.
This is the third human infection with novel influenza A virus that has occurred during the 2021-22 influenza season in the United States. One influenza A(H3N2) variant virus infection was reported by Ohio and one influenza A(H1) variant virus (neuraminidase not determined) infection was reported by Oklahoma.
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus”. Most human infections with variant influenza viruses occur following close proximity to swine, but person-to-person transmission can occur. In most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person. Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully understood and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza virus infection in humans, and strategies to interact safely with swine can be found at www.cdc.gov/flu/swineflu/index.htm. Additional information regarding human infections with novel influenza A viruses can be found at http://gis.cdc.gov/grasp/fluview/Novel_Influenza.html.
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 618 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve. Virus antigenic data will be reported later this season when a sufficient number of specimens have been tested.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 6, 1.4% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. One of the 10 HHS regions (Region 7) is above its region-specific baseline, and the remaining regions are below their baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet in week 6 remained stable among children 0–4 years of age and decreased for all other age groups (5–24 years, 25-49 years, 50–64 years, and 65+ years) compared to week 5.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 6, 57 (0.4%) of 14,248 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,382 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 12, 2022. The overall cumulative hospitalization rate is 4.7 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 6 during the 2020-2021 season (0.6 per 100,000), but lower than the in-season rates observed in week 6 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 23.8 to 67.9 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged ≥65 years (12.5); within this group, rates were highest among adults aged ≥85 years (26.2). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (6.9) followed by adults aged 50-64 years (4.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (6.4), followed by non-Hispanic Black persons (5.9).
Among 1,382 hospitalizations, 1,300 (94.1%) were associated with influenza A virus, 72 (5.2%) with influenza B virus, 5 (0.4%) with influenza A virus and influenza B virus co-infection, and 5 (0.4%) with influenza virus for which the type was not determined. Among 339 hospitalizations with influenza A subtype information, 336 (99.1%) were A(H3N2), and 3 (0.9%) were A(H1N1)pdm09. Based on preliminary data, of the 1,382 laboratory-confirmed influenza-associated hospitalizations, 3.3% also tested positive for SARS-CoV-2.
Among 664 hospitalized adults with information on underlying medical conditions, 91% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 59 hospitalized children with information on underlying medical conditions, 69.5% had at least one reported underlying medical condition; the most commonly reported was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 6, 1,073 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS-Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance. The increase in hospitalizations reported during week 6 may be due in part to the increase in reporting facilities.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 17, 2022, 22.6% of the deaths that occurred during the week ending February 12, 2022 (week 6), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 4,116 PIC deaths reported for this week, 3,447 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 17 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 6.
A total of five influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 18, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated February 18, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 6, ending February 12, 2022
Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
Viruses
Clinical Lab3.0%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.4%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 0 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.4%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.7 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,073
patients admitted to hospitals with influenza
this week.
NCHS Mortality22.6%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week, with a total of 5 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
- The percentage of outpatient visits due to respiratory illness decreased nationally again this week and is below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect increased slightly this week.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- CDC estimates that so far this season there have been at least 2.3 million flu illnesses, 22,000 hospitalizations, and 1,300 deaths from flu.
- An annual flu vaccine is the best way to protect against flu and its potentially serious complications. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccination coverage remains lower this season compared to last.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 7,201 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 433 (6.0%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 44,436 | 1,569,698 |
| No. of positive specimens (%) | 1,324 (3.0%) | 40,934 (2.6%) |
| Positive specimens by type | ||
| Influenza A | 1,300 (98.2%) | 39,971 (97.6%) |
| Influenza B | 24 (1.8%) | 963 (2.4%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 25,675 | 613,185 |
| No. of positive specimens | 454 | 12,446 |
| Positive specimens by type/subtype | ||
| Influenza A | 453 (99.8%) | 12,349 (99.2%) |
| (H1N1)pdm09 | 0 | 4 (<0.1%) |
| H3N2 | 146 (100%) | 8,376 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 307 | 3,968 |
| Influenza B | 1 (0.2%) | 97 (0.8%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 1 | 63 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Novel Influenza A Virus
One human infection with a novel influenza A (H1N2) variant virus was reported by California. The infection occurred in an adult ≥ 18 years of age. The patient was not hospitalized and has recovered from their illness. The patient had direct contact with swine prior to specimen collection. Respiratory illness was reported among contacts of the patient, however this occurred during a period of high respiratory illness activity and no specimens from the contacts were received for testing. No ongoing person-to-person transmission has been identified associated with this case.
This is the third human infection with novel influenza A virus that has occurred during the 2021-22 influenza season in the United States. One influenza A(H3N2) variant virus infection was reported by Ohio and one influenza A(H1) variant virus (neuraminidase not determined) infection was reported by Oklahoma.
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus”. Most human infections with variant influenza viruses occur following close proximity to swine, but person-to-person transmission can occur. In most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person. Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully understood and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza virus infection in humans, and strategies to interact safely with swine can be found at www.cdc.gov/flu/swineflu/index.htm. Additional information regarding human infections with novel influenza A viruses can be found at http://gis.cdc.gov/grasp/fluview/Novel_Influenza.html.
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 618 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve. Virus antigenic data will be reported later this season when a sufficient number of specimens have been tested.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 595 | ||||
| 3C.2a1b | 595 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 593 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 20 | ||||
| V1A | 20 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (45.0%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 11 (55.0%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 658 | 3 | 635 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 658 | 3 | 635 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 658 | 3 | 635 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 650 | 3 | 627 | 20 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 6, 1.4% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. One of the 10 HHS regions (Region 7) is above its region-specific baseline, and the remaining regions are below their baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet in week 6 remained stable among children 0–4 years of age and decreased for all other age groups (5–24 years, 25-49 years, 50–64 years, and 65+ years) compared to week 5.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 6 (Week ending Feb. 12, 2022) | Week 5 (Week ending Feb. 5, 2022) | Week 6 (Week ending Feb. 12, 2022) | Week 5 (Week ending Feb. 5, 2022) | |
| Very High | 0 | 0 | 4 | 2 |
| High | 0 | 0 | 1 | 6 |
| Moderate | 0 | 4 | 10 | 21 |
| Low | 8 | 3 | 51 | 66 |
| Minimal | 45 | 47 | 593 | 563 |
| Insufficient Data | 2 | 1 | 270 | 271 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 6, 57 (0.4%) of 14,248 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,382 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 12, 2022. The overall cumulative hospitalization rate is 4.7 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 6 during the 2020-2021 season (0.6 per 100,000), but lower than the in-season rates observed in week 6 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 23.8 to 67.9 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged ≥65 years (12.5); within this group, rates were highest among adults aged ≥85 years (26.2). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (6.9) followed by adults aged 50-64 years (4.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (6.4), followed by non-Hispanic Black persons (5.9).
Among 1,382 hospitalizations, 1,300 (94.1%) were associated with influenza A virus, 72 (5.2%) with influenza B virus, 5 (0.4%) with influenza A virus and influenza B virus co-infection, and 5 (0.4%) with influenza virus for which the type was not determined. Among 339 hospitalizations with influenza A subtype information, 336 (99.1%) were A(H3N2), and 3 (0.9%) were A(H1N1)pdm09. Based on preliminary data, of the 1,382 laboratory-confirmed influenza-associated hospitalizations, 3.3% also tested positive for SARS-CoV-2.
Among 664 hospitalized adults with information on underlying medical conditions, 91% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 59 hospitalized children with information on underlying medical conditions, 69.5% had at least one reported underlying medical condition; the most commonly reported was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 6, 1,073 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS-Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance. The increase in hospitalizations reported during week 6 may be due in part to the increase in reporting facilities.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 17, 2022, 22.6% of the deaths that occurred during the week ending February 12, 2022 (week 6), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 4,116 PIC deaths reported for this week, 3,447 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 17 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 6.
A total of five influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 18, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
FluView Summary ending on February 19, 2022
Updated February 25, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 7, ending February 19, 2022
Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
Viruses
Clinical Lab4.2%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.5%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.4%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.9 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,420
patients admitted to hospitals with influenza
this week.
NCHS Mortality20.4%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths1
influenza-associated deaths reported this week, with a total of 6 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 7,560 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 456 (6.0%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 641 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 7, 1.5% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. All 10 HHS regions are below their region-specific baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet in week 7 increased among one age group (5–24 years) compared to week 6. The percentage of visits for respiratory illness in the other age groups (0–4 years, 25-49 years, 50–64 years, and 65+ years) continues to trend downwards.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 7, 58 (0.4%) of 14,243 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,441 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 19, 2022. The overall cumulative hospitalization rate was 4.9 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 7 during the 2020-2021 season (0.6 per 100,000), but lower than the in-season rates observed in week 7 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 27.4 to 74.5 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (12.9). Among adults aged ≥65 years, rates were highest among adults aged ≥85 (27.3). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (7.1) followed by adults aged 50-64 years (4.7). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (6.4), followed by non-Hispanic Black persons (6.2).
Among 1,441 hospitalizations, 1,358 (94.2%) were associated with influenza A virus, 76 (5.3%) with influenza B virus, 4 (0.3%) with influenza A virus and influenza B virus co-infection, and 3 (0.2%) with influenza virus for which the type was not determined. Among 353 hospitalizations with influenza A subtype information, 349 (98.9%) were A(H3N2), and 4 (1.1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,441 laboratory-confirmed influenza-associated hospitalizations, 3.5% also tested positive for SARS-CoV-2.
Among 713 hospitalized adults with information on underlying medical conditions, 90% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 62 hospitalized children with information on underlying medical conditions, 69.4% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 7, 1,420 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS-Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 24, 2022, 20.4% of the deaths that occurred during the week ending February 19, 2022 (week 7), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 3,185 PIC deaths reported for this week, 2,587 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
One influenza-associated pediatric death occurring during the 2021-2022 season was reported to CDC during week 7. This death was associated with an influenza A virus for which no subtyping was performed and occurred during week 7.
A total of six influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 25, 2022, 11:00 AM
Updated February 25, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 7, ending February 19, 2022
Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
Viruses
Clinical Lab4.2%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.5%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.4%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET4.9 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,420
patients admitted to hospitals with influenza
this week.
NCHS Mortality20.4%
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths1
influenza-associated deaths reported this week, with a total of 6 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data, now included in FluView, show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness remained stable nationally compared to last week and is below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased for the past three weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- One influenza-associated pediatric death was reported this week. This is the sixth pediatric death reported this season.
- CDC estimates that so far this season there have been at least 2.4 million flu illnesses, 23,000 hospitalizations, and 1,400 deaths from flu.
- An annual flu vaccine is the best way to protect against flu and its potentially serious complications. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccination coverage remains lower this season compared to last.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 7,560 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 456 (6.0%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 43,078 | 1,634,117 |
| No. of positive specimens (%) | 1,807 (4.2%) | 43,153 (2.6%) |
| Positive specimens by type | ||
| Influenza A | 1,770 (98.0%) | 42,137 (97.6%) |
| Influenza B | 37 (2.0%) | 1,016 (2.4%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 18,582 | 632,699 |
| No. of positive specimens | 366 | 12,971 |
| Positive specimens by type/subtype | ||
| Influenza A | 365 (99.7%) | 12,873 (99.2%) |
| (H1N1)pdm09 | 0 | 4 (<0.1%) |
| H3N2 | 92 (100%) | 8,619 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 273 | 4,249 |
| Influenza B | 1 (0.3%) | 98 (0.8%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 1 | 64 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 641 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 618 | ||||
| 3C.2a1b | 618 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 616 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 20 | ||||
| V1A | 20 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (45.0%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 11 (55.0%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
- A (H1N1)pdm09: Two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 1 (50%) was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 1 (50%) was well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of fifty-eight A(H3N2) viruses were antigenically characterized by HINT, and 2 (3%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 18 (31%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Thirteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (85%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (85%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 658 | 3 | 635 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 658 | 3 | 635 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 658 | 3 | 635 | 20 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 650 | 3 | 627 | 20 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 7, 1.5% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. All 10 HHS regions are below their region-specific baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet in week 7 increased among one age group (5–24 years) compared to week 6. The percentage of visits for respiratory illness in the other age groups (0–4 years, 25-49 years, 50–64 years, and 65+ years) continues to trend downwards.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 7 (Week ending Feb. 19, 2022) | Week 6 (Week ending Feb. 12, 2022) | Week 7 (Week ending Feb. 19, 2022) | Week 6 (Week ending Feb. 12, 2022) | |
| Very High | 0 | 0 | 4 | 4 |
| High | 0 | 0 | 1 | 2 |
| Moderate | 2 | 0 | 17 | 10 |
| Low | 3 | 8 | 40 | 52 |
| Minimal | 48 | 46 | 594 | 602 |
| Insufficient Data | 2 | 1 | 273 | 259 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 7, 58 (0.4%) of 14,243 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,441 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 19, 2022. The overall cumulative hospitalization rate was 4.9 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 7 during the 2020-2021 season (0.6 per 100,000), but lower than the in-season rates observed in week 7 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 27.4 to 74.5 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (12.9). Among adults aged ≥65 years, rates were highest among adults aged ≥85 (27.3). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (7.1) followed by adults aged 50-64 years (4.7). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (6.4), followed by non-Hispanic Black persons (6.2).
Among 1,441 hospitalizations, 1,358 (94.2%) were associated with influenza A virus, 76 (5.3%) with influenza B virus, 4 (0.3%) with influenza A virus and influenza B virus co-infection, and 3 (0.2%) with influenza virus for which the type was not determined. Among 353 hospitalizations with influenza A subtype information, 349 (98.9%) were A(H3N2), and 4 (1.1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,441 laboratory-confirmed influenza-associated hospitalizations, 3.5% also tested positive for SARS-CoV-2.
Among 713 hospitalized adults with information on underlying medical conditions, 90% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 62 hospitalized children with information on underlying medical conditions, 69.4% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS-Protect Hospitalization Surveillance
Hospitals report to HHS-Protect the number of patients admitted with laboratory-confirmed influenza. During week 7, 1,420 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS-Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on February 24, 2022, 20.4% of the deaths that occurred during the week ending February 19, 2022 (week 7), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 3,185 PIC deaths reported for this week, 2,587 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
One influenza-associated pediatric death occurring during the 2021-2022 season was reported to CDC during week 7. This death was associated with an influenza A virus for which no subtyping was performed and occurred during week 7.
A total of six influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: February 25, 2022, 11:00 AM
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated March 4, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 8, ending February 26, 2022
Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
Viruses
Clinical Lab4.1%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.5%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 0 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.5%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET5.2 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,504
patients admitted to hospitals with influenza
this week.
NCHS Mortality16.7 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths2
influenza-associated deaths reported this week, with a total of 8 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,064 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 491 (6.1%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 641 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 8, 1.5% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet in week 8 increased among one age group (0-4 years) compared to week 7 while all other age groups (5-24 years, 25-49 years, 50–64 years, and 65+ years) remained stable.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 8, 69 (0.5%) of 14,200 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,514 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 26, 2022. The overall cumulative hospitalization rate was 5.2 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 8 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 8 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 32.1 to 81.7 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (13.5). Among adults aged 65 and older, rates were highest among adults aged 85 and older (28.3). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (7.7), followed by adults aged 50-64 years (4.8). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (6.6), followed by non-Hispanic American Indian or Alaska Native persons (6.4).
Among 1,514 hospitalizations, 1,429 (94.4%) were associated with influenza A virus, 80 (5.3%) with influenza B virus, 4 (0.3%) with influenza A virus and influenza B virus co-infection, and 1 (0.1%) with influenza virus for which the type was not determined. Among 383 hospitalizations with influenza A subtype information, 379 (99%) were A(H3N2), and 4 (1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,514 laboratory-confirmed influenza-associated hospitalizations, 3.9% also tested positive for SARS-CoV-2.
Among 768 hospitalized adults with information on underlying medical conditions, 90.4% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 66 hospitalized children with information on underlying medical conditions, 71.2% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 8, 1,504 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 3, 2022, 16.7% of the deaths that occurred during the week ending February 26, 2022 (week 8), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 3,075 PIC deaths reported for this week, 2,274 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths occurring in weeks 47 (the week ending November 27, 2021) and 7 (the week ending February 19, 2022) of the 2021-2022 season were reported to CDC during week 8. Both deaths were associated with influenza A viruses for which no subtyping was performed.
A total of eight influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 4, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/
Updated March 4, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 8, ending February 26, 2022
Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
Viruses
Clinical Lab4.1%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.5%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 0 jurisdictions experienced moderate activity and 0 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.5%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET5.2 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,504
patients admitted to hospitals with influenza
this week.
NCHS Mortality16.7 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths2
influenza-associated deaths reported this week, with a total of 8 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Sporadic influenza activity continues across the country. In some areas, influenza activity is increasing.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness remained stable nationally for the third consecutive week and is below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased for the past four weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- Two influenza-associated pediatric deaths were reported this week. There has been a total of eight pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 2.5 million flu illnesses, 24,000 hospitalizations, and 1,400 deaths from flu.
- An annual flu vaccine is the best way to protect against flu and its potentially serious complications. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccination coverage remains lower this season compared to last.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,064 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 491 (6.1%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 35,541 | 1,690,086 |
| No. of positive specimens (%) | 1,462 (4.1%) | 45,388 (2.7%) |
| Positive specimens by type | ||
| Influenza A | 1,445 (98.8%) | 44,338 (97.7%) |
| Influenza B | 17 (1.2%) | 1,050 (2.3%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 17,331 | 654,844 |
| No. of positive specimens | 293 | 13,523 |
| Positive specimens by type/subtype | ||
| Influenza A | 291 (99.3%) | 13,423 (99.3%) |
| (H1N1)pdm09 | 0 | 4 (<0.1%) |
| H3N2 | 106 (100%) | 8,943 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 185 | 4,475 |
| Influenza B | 2 (0.7%) | 100 (0.7%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 2 | 66 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 641 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 709 | ||||
| 3C.2a1b | 709 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 707 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 21 | ||||
| V1A | 21 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (43.0%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 12 (57.0%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
- A (H1N1)pdm09: Two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 1 (50%) was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 1 (50%) was well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of fifty-eight A(H3N2) viruses were antigenically characterized by HINT, and 2 (3%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 18 (31%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Thirteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (85%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (85%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 749 | 3 | 725 | 21 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 749 | 3 | 725 | 21 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 749 | 3 | 725 | 21 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 739 | 3 | 715 | 21 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 8, 1.5% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet in week 8 increased among one age group (0-4 years) compared to week 7 while all other age groups (5-24 years, 25-49 years, 50–64 years, and 65+ years) remained stable.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 8 (Week ending Feb. 26, 2022) | Week 7 (Week ending Feb. 19, 2022) | Week 8 (Week ending Feb. 26, 2022) | Week 7 (Week ending Feb. 19, 2022) | |
| Very High | 0 | 0 | 3 | 4 |
| High | 0 | 0 | 4 | 1 |
| Moderate | 0 | 1 | 13 | 17 |
| Low | 6 | 4 | 43 | 41 |
| Minimal | 46 | 48 | 597 | 606 |
| Insufficient Data | 3 | 2 | 269 | 260 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 8, 69 (0.5%) of 14,200 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,514 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and February 26, 2022. The overall cumulative hospitalization rate was 5.2 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 8 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 8 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 32.1 to 81.7 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (13.5). Among adults aged 65 and older, rates were highest among adults aged 85 and older (28.3). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (7.7), followed by adults aged 50-64 years (4.8). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (6.6), followed by non-Hispanic American Indian or Alaska Native persons (6.4).
Among 1,514 hospitalizations, 1,429 (94.4%) were associated with influenza A virus, 80 (5.3%) with influenza B virus, 4 (0.3%) with influenza A virus and influenza B virus co-infection, and 1 (0.1%) with influenza virus for which the type was not determined. Among 383 hospitalizations with influenza A subtype information, 379 (99%) were A(H3N2), and 4 (1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,514 laboratory-confirmed influenza-associated hospitalizations, 3.9% also tested positive for SARS-CoV-2.
Among 768 hospitalized adults with information on underlying medical conditions, 90.4% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 66 hospitalized children with information on underlying medical conditions, 71.2% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 8, 1,504 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 3, 2022, 16.7% of the deaths that occurred during the week ending February 26, 2022 (week 8), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 3,075 PIC deaths reported for this week, 2,274 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths occurring in weeks 47 (the week ending November 27, 2021) and 7 (the week ending February 19, 2022) of the 2021-2022 season were reported to CDC during week 8. Both deaths were associated with influenza A viruses for which no subtyping was performed.
A total of eight influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 4, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/
sharon sanders
Editor-in-Chief & President
bump this
sharon sanders
Editor-in-Chief & President
FluView Summary ending on March 5, 2022
Updated March 11, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 9, ending March 5, 2022
Influenza activity is increasing in most of the country.
Viruses
Clinical Lab5.8%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.6%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 1 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.5%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET5.5 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,772
patients admitted to hospitals with influenza
this week.
NCHS Mortality13.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths2
influenza-associated deaths reported this week for a total of 10 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza activity is increasing again in most of the country with the largest increases being reported in the central and south-central parts of the country (Regions 6 and 7). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,330 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 491 (5.9%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 768 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
2022-2023 Influenza Season – U.S. Influenza Vaccine Composition:
The World Health Organization (WHO) has recommended the Northern Hemisphere 2022-2023 influenza vaccine composition, and the Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) subsequently made the influenza vaccine composition recommendation for the United States. Both agencies recommend that influenza vaccines contain the following:
Assessment of Virus Susceptibility to Antiviral Medications
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 9, 1.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
There is an increasing trend in the percentage of visits for respiratory illness reported in ILINet among one age group (5-24 years), while it remained stable for all other age groups (25-49 years, 50–64 years, and 65+ years) compared to week 8.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 9, 73 (0.5%) of 14,217 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,625 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 5, 2022. The overall cumulative hospitalization rate was 5.5 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 9 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 9 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 36.6 to 86.3 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (14.7). Among adults aged 65 and older, rates were highest among adults aged 85 and older (30.4). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (8.0) followed by adults aged 50-64 years (5.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (7.0), followed by non-Hispanic American Indian or Alaska Native persons (6.4).
Among 1,625 hospitalizations, 1,536 (94.5%) were associated with influenza A virus, 82 (5%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 3 (0.2%) with influenza virus for which the type was not determined. Among 405 hospitalizations with influenza A subtype information, 401 (99%) were A(H3N2), and 4 (1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,625 laboratory-confirmed influenza-associated hospitalizations, 3.9% also tested positive for SARS-CoV-2.
Among 813 hospitalized adults with information on underlying medical conditions, 92.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 76 hospitalized children with information on underlying medical conditions, 71.1% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 9, 1,772 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 10, 2022, 13.1% of the deaths that occurred during the week ending March 5, 2022 (week 9), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 2,448 PIC deaths reported for this week, 1,675 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 9. One death was associated with an influenza A (H3) virus and occurred during week 4 (the week ending January 29, 2022). The other death was associated with an influenza A virus for which no subtyping was performed and occurred during week 7 (the week ending February 19, 2022).
A total of ten influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 11, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/weeklyarchives2021-2022/week09.htm
Updated March 11, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 9, ending March 5, 2022
Influenza activity is increasing in most of the country.
Viruses
Clinical Lab5.8%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.6%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 1 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.5%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET5.5 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations1,772
patients admitted to hospitals with influenza
this week.
NCHS Mortality13.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths2
influenza-associated deaths reported this week for a total of 10 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity is increasing in most of the country.
- The highest influenza percent positivity levels were seen in states in the central and south-central regions of the country.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness increased slightly this week but is still below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past five weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- Two influenza-associated pediatric deaths were reported this week. There have been 10 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 2.7 million flu illnesses, 26,000 hospitalizations, and 1,500 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza activity is increasing again in most of the country with the largest increases being reported in the central and south-central parts of the country (Regions 6 and 7). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,330 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 491 (5.9%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 420,274 | 1,755,040 |
| No. of positive specimens (%) | 2,446 (5.8%) | 48,942 (2.8%) |
| Positive specimens by type | ||
| Influenza A | 2,438 (99.7%) | 47,875 (97.8%) |
| Influenza B | 8 (0.3%) | 1,067 (2.2%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 13,815 | 669,426 |
| No. of positive specimens | 321 | 14,003 |
| Positive specimens by type/subtype | ||
| Influenza A | 319 (99.4%) | 13,901 (99.3%) |
| (H1N1)pdm09 | 0 | 5 (0.1%) |
| H3N2 | 153 (100%) | 9,278 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 166 | 4,617 |
| Influenza B | 2 (0.6%) | 102 (0.7%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 2 | 68 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 768 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 744 | ||||
| 3C.2a1b | 744 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 742 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 21 | ||||
| V1A | 21 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (43.0%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 12 (57.0%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
- A (H1N1)pdm09: Two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 1 (50%) was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 1 (50%) was well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of fifty-eight A(H3N2) viruses were antigenically characterized by HINT, and 2 (3%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 18 (31%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Thirteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (85%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (85%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
2022-2023 Influenza Season – U.S. Influenza Vaccine Composition:
The World Health Organization (WHO) has recommended the Northern Hemisphere 2022-2023 influenza vaccine composition, and the Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) subsequently made the influenza vaccine composition recommendation for the United States. Both agencies recommend that influenza vaccines contain the following:
- Egg-based vaccines
- an A/Victoria/2570/2019 (H1N1)pdm09-like virus
- an A/Darwin/9/2021 (H3N2)-like virus
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus
- a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus
- Cell culture- or recombinant-based vaccines
- an A/Wisconsin/588/2019 (H1N1)pdm09-like virus
- an A/Darwin/6/2021 (H3N2)-like virus
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus
- a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus
Assessment of Virus Susceptibility to Antiviral Medications
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 784 | 3 | 760 | 21 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 784 | 3 | 760 | 21 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 784 | 3 | 760 | 21 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 772 | 3 | 748 | 21 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 9, 1.6% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
There is an increasing trend in the percentage of visits for respiratory illness reported in ILINet among one age group (5-24 years), while it remained stable for all other age groups (25-49 years, 50–64 years, and 65+ years) compared to week 8.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 9 (Week ending Mar. 5, 2022) | Week 8 (Week ending Feb. 26, 2022) | Week 9 (Week ending Mar. 5, 2022) | Week 8 (Week ending Feb. 26, 2022) | |
| Very High | 0 | 0 | 3 | 2 |
| High | 1 | 0 | 5 | 4 |
| Moderate | 2 | 0 | 12 | 13 |
| Low | 5 | 5 | 48 | 44 |
| Minimal | 44 | 49 | 589 | 606 |
| Insufficient Data | 3 | 1 | 272 | 260 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 9, 73 (0.5%) of 14,217 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,625 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 5, 2022. The overall cumulative hospitalization rate was 5.5 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 9 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 9 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 36.6 to 86.3 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (14.7). Among adults aged 65 and older, rates were highest among adults aged 85 and older (30.4). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (8.0) followed by adults aged 50-64 years (5.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (7.0), followed by non-Hispanic American Indian or Alaska Native persons (6.4).
Among 1,625 hospitalizations, 1,536 (94.5%) were associated with influenza A virus, 82 (5%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 3 (0.2%) with influenza virus for which the type was not determined. Among 405 hospitalizations with influenza A subtype information, 401 (99%) were A(H3N2), and 4 (1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,625 laboratory-confirmed influenza-associated hospitalizations, 3.9% also tested positive for SARS-CoV-2.
Among 813 hospitalized adults with information on underlying medical conditions, 92.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 76 hospitalized children with information on underlying medical conditions, 71.1% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 9, 1,772 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 10, 2022, 13.1% of the deaths that occurred during the week ending March 5, 2022 (week 9), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 2,448 PIC deaths reported for this week, 1,675 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 12 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 9. One death was associated with an influenza A (H3) virus and occurred during week 4 (the week ending January 29, 2022). The other death was associated with an influenza A virus for which no subtyping was performed and occurred during week 7 (the week ending February 19, 2022).
A total of ten influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 11, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/weeklyarchives2021-2022/week09.htm
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated March 18, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 10, ending March 12, 2022
Influenza activity is increasing in most of the country.
Viruses
Clinical Lab6.8%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.7%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 1 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET5.9 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,082
patients admitted to hospitals with influenza
this week.
NCHS Mortality10.8 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths3
influenza-associated deaths reported this week for a total of 13 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza activity is increasing again in most of the country with the largest increases being reported in the central and south-central parts of the country (Regions 6 and 7). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,408 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 473 (5.6%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 817 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 10, 1.7% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
In week 10, the percentage of visits for respiratory illness reported in ILINet increased among two age groups (0–4 years and 5–24 years), while remaining stable for all other age groups (25–49 years, 50–64 years, and 65+ years) compared to week 9.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 10, 94 (0.7%) of 14,266 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,734 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 12, 2022. The overall cumulative hospitalization rate was 5.9 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 10 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 10 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 41.3 to 89.9 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (15.9). Among adults aged 65 and older, rates were highest among adults aged 85 and older (32.4). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (8.5) followed by adults aged 50-64 years (5.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (7.3), followed by non-Hispanic American Indian or Alaska Native persons (6.9).
Among 1,734 hospitalizations, 1,641 (94.6%) were associated with influenza A virus, 86 (5%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 3 (0.2%) with influenza virus for which the type was not determined. Among 433 hospitalizations with influenza A subtype information, 428 (98.8%) were A(H3N2), and 5 (1.2%) were A(H1N1)pdm09. Based on preliminary data, of the 1,734 laboratory-confirmed influenza-associated hospitalizations, 3.9% also tested positive for SARS-CoV-2.
Among 875 hospitalized adults with information on underlying medical conditions, 92.8% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 97 hospitalized children with information on underlying medical conditions, 71.1% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 10, 2,082 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 17, 2022, 10.8% of the deaths that occurred during the week ending March 12, 2022 (week 10), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 1,890 PIC deaths reported for this week, 1,215 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 15 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Three influenza-associated pediatric deaths were reported to CDC during week 10. The deaths occurred in weeks 3, 8, and 9 of the 2021-2022 season (weeks ending January 22, February 26, and March 5, 2022, respectively). All three deaths were associated with influenza A viruses for which no subtyping was performed.
A total of 13 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 18, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated March 18, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 10, ending March 12, 2022
Influenza activity is increasing in most of the country.
Viruses
Clinical Lab6.8%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.7%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 1 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET5.9 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,082
patients admitted to hospitals with influenza
this week.
NCHS Mortality10.8 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths3
influenza-associated deaths reported this week for a total of 13 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity is increasing in most of the country.
- The highest levels of influenza percent positivity from clinical labs were seen in states in the central and south-central regions of the country.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness increased slightly this week but is still below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past six weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- Three influenza-associated pediatric deaths were reported this week. There have been 13 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 2.9 million flu illnesses, 28,000 hospitalizations, and 1,700 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza activity is increasing again in most of the country with the largest increases being reported in the central and south-central parts of the country (Regions 6 and 7). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,408 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 473 (5.6%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 39,267 | 1,819,313 |
| No. of positive specimens (%) | 2,685 (6.8%) | 53,042 (2.9%) |
| Positive specimens by type | ||
| Influenza A | 2,655 (98.9%) | 51,897 (97.8%) |
| Influenza B | 30 (1.1%) | 1,145 (2.2%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 12,542 | 683,949 |
| No. of positive specimens | 347 | 14,558 |
| Positive specimens by type/subtype | ||
| Influenza A | 347 (100%) | 14,456 (99.3%) |
| (H1N1)pdm09 | 0 | 5 (0.1%) |
| H3N2 | 196 (100%) | 9,714 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 151 | 4,736 |
| Influenza B | 0 (0%) | 102 (0.7%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 0 | 68 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 817 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 3 | ||||
| 6B.1A | 3 (100%) | 5a.1 | 2 (66.7%) | ||
| 5a.2 | 1 (33.3%) | ||||
| A/H3 | 791 | ||||
| 3C.2a1b | 791 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 789 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
- A (H1N1)pdm09: Two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 1 (50%) was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 1 (50%) was well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of fifty-eight A(H3N2) viruses were antigenically characterized by HINT, and 2 (3%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 18 (31%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fourteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (79%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (79%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 833 | 3 | 807 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 833 | 3 | 807 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 833 | 3 | 807 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 819 | 3 | 793 | 23 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) |
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 10, 1.7% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
In week 10, the percentage of visits for respiratory illness reported in ILINet increased among two age groups (0–4 years and 5–24 years), while remaining stable for all other age groups (25–49 years, 50–64 years, and 65+ years) compared to week 9.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 10 (Week ending Mar. 12, 2022) | Week 9 (Week ending Mar. 5, 2022) | Week 10 (Week ending Mar. 12, 2022) | Week 9 (Week ending Mar. 5, 2022) | |
| Very High | 0 | 0 | 3 | 3 |
| High | 1 | 1 | 5 | 4 |
| Moderate | 2 | 1 | 23 | 11 |
| Low | 5 | 6 | 54 | 51 |
| Minimal | 46 | 44 | 573 | 597 |
| Insufficient Data | 1 | 3 | 271 | 263 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 10, 94 (0.7%) of 14,266 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,734 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 12, 2022. The overall cumulative hospitalization rate was 5.9 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 10 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 10 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 41.3 to 89.9 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (15.9). Among adults aged 65 and older, rates were highest among adults aged 85 and older (32.4). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (8.5) followed by adults aged 50-64 years (5.4). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (7.3), followed by non-Hispanic American Indian or Alaska Native persons (6.9).
Among 1,734 hospitalizations, 1,641 (94.6%) were associated with influenza A virus, 86 (5%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 3 (0.2%) with influenza virus for which the type was not determined. Among 433 hospitalizations with influenza A subtype information, 428 (98.8%) were A(H3N2), and 5 (1.2%) were A(H1N1)pdm09. Based on preliminary data, of the 1,734 laboratory-confirmed influenza-associated hospitalizations, 3.9% also tested positive for SARS-CoV-2.
Among 875 hospitalized adults with information on underlying medical conditions, 92.8% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 97 hospitalized children with information on underlying medical conditions, 71.1% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 10, 2,082 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 17, 2022, 10.8% of the deaths that occurred during the week ending March 12, 2022 (week 10), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.2% for this week. Among the 1,890 PIC deaths reported for this week, 1,215 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 15 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Three influenza-associated pediatric deaths were reported to CDC during week 10. The deaths occurred in weeks 3, 8, and 9 of the 2021-2022 season (weeks ending January 22, February 26, and March 5, 2022, respectively). All three deaths were associated with influenza A viruses for which no subtyping was performed.
A total of 13 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 18, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
bump this
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated March 25, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 11, ending March 19, 2022
Influenza activity is increasing in most of the country.
Viruses
Clinical Lab7.7%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.8%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 7 jurisdictions experienced moderate activity and 1 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET6.5 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,733
patients admitted to hospitals with influenza
this week.
NCHS Mortality9.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week for a total of 13 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza activity is increasing again in most of the country with the largest increases being reported in the central and south-central parts of the country (Regions 6 and 7). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,700 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 476 (5.5%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 839 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 11, 1.8% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
In week 11, the percentage of visits for respiratory illness reported in ILINet increased among two age groups (0–4 years and 5–24 years), while remaining stable for all other age groups (25–49 years, 50–64 years, and 65+ years) compared to week 10.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 11, 95 (0.7%) of 14,249 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,905 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 19, 2022. The overall cumulative hospitalization rate was 6.5 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 11 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 11 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 47.1 to 93.5 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (17.6). Among adults aged 65 and older, rates were highest among adults aged 85 and older (35.7). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (9.2) followed by adults aged 50-64 years (6.0). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (9.8), followed by non-Hispanic Black persons (7.8).
Among 1,905 hospitalizations, 1,802 (94.6%) were associated with influenza A virus, 90 (4.7%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 9 (0.5%) with influenza virus for which the type was not determined. Among 477 hospitalizations with influenza A subtype information, 472 (99%) were A(H3N2), and 5 (1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,905 laboratory-confirmed influenza-associated hospitalizations, 3.5% also tested positive for SARS-CoV-2.
Among 973 hospitalized adults with information on underlying medical conditions, 92.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 117 hospitalized children with information on underlying medical conditions, 74.4% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 11, 2,733 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 24, 2022, 9.1% of the deaths that occurred during the week ending March 19, 2022 (week 11), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.1% for this week. Among the 1,788 PIC deaths reported for this week, 928 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 17 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 11.
A total of 13 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 25, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated March 25, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 11, ending March 19, 2022
Influenza activity is increasing in most of the country.
Viruses
Clinical Lab7.7%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.8%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 7 jurisdictions experienced moderate activity and 1 jurisdictions experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET6.5 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,733
patients admitted to hospitals with influenza
this week.
NCHS Mortality9.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths0
influenza-associated deaths reported this week for a total of 13 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity is increasing in most of the country.
- The highest levels of influenza percent positivity from clinical labs were seen in states in the central and south-central regions of the country.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness increased slightly this week but is still below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past seven weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- CDC estimates that, so far this season, there have been at least 3.1 million flu illnesses, 31,000 hospitalizations, and 1,800 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza activity is increasing again in most of the country with the largest increases being reported in the central and south-central parts of the country (Regions 6 and 7). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 8,700 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 476 (5.5%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 42,370 | 1,879,003 |
| No. of positive specimens (%) | 3,248 (7.7%) | 57,475 (3.1%) |
| Positive specimens by type | ||
| Influenza A | 3,220 (99.1%) | 56,257 (97.9%) |
| Influenza B | 28 (0.9%) | 1,218 (2.1%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 11,958 | 697,940 |
| No. of positive specimens | 337 | 15,178 |
| Positive specimens by type/subtype | ||
| Influenza A | 337 (100%) | 15,076 (99.3%) |
| (H1N1)pdm09 | 0 | 5 (<0.1%) |
| H3N2 | 174 (100%) | 10,180 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 163 | 4,890 |
| Influenza B | 0 (0%) | 102 (0.7%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 0 | 68 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 839 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 4 | ||||
| 6B.1A | 4 (100%) | 5a.1 | 2 (50%) | ||
| 5a.2 | 2 (50%) | ||||
| A/H3 | 812 | ||||
| 3C.2a1b | 812 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 810 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Influenza A Viruses
- A (H1N1)pdm09: Two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 1 (50%) was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 1 (50%) was well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of 61 A(H3N2) viruses were antigenically characterized by HINT, and 2 (3%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 18 (30%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fourteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (79%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (79%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 898 | 4 | 871 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 898 | 4 | 871 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 898 | 4 | 871 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 888 | 4 | 861 | 23 | 0 |
| Reduced Susceptibility | (0.0%) | (0.0%) | 1 (0.1%) | (0.0%) | (0.0%) |
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 11, 1.8% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
In week 11, the percentage of visits for respiratory illness reported in ILINet increased among two age groups (0–4 years and 5–24 years), while remaining stable for all other age groups (25–49 years, 50–64 years, and 65+ years) compared to week 10.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 11 (Week ending Mar. 19, 2022) | Week 10 (Week ending Mar. 12, 2022) | Week 11 (Week ending Mar. 19, 2022) | Week 10 (Week ending Mar. 12, 2022) | |
| Very High | 0 | 0 | 1 | 3 |
| High | 1 | 1 | 9 | 6 |
| Moderate | 7 | 3 | 15 | 22 |
| Low | 1 | 4 | 76 | 57 |
| Minimal | 44 | 47 | 556 | 581 |
| Insufficient Data | 2 | 0 | 272 | 260 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 11, 95 (0.7%) of 14,249 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 1,905 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 19, 2022. The overall cumulative hospitalization rate was 6.5 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 11 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 11 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 47.1 to 93.5 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (17.6). Among adults aged 65 and older, rates were highest among adults aged 85 and older (35.7). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (9.2) followed by adults aged 50-64 years (6.0). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (9.8), followed by non-Hispanic Black persons (7.8).
Among 1,905 hospitalizations, 1,802 (94.6%) were associated with influenza A virus, 90 (4.7%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 9 (0.5%) with influenza virus for which the type was not determined. Among 477 hospitalizations with influenza A subtype information, 472 (99%) were A(H3N2), and 5 (1%) were A(H1N1)pdm09. Based on preliminary data, of the 1,905 laboratory-confirmed influenza-associated hospitalizations, 3.5% also tested positive for SARS-CoV-2.
Among 973 hospitalized adults with information on underlying medical conditions, 92.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 117 hospitalized children with information on underlying medical conditions, 74.4% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 11, 2,733 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 24, 2022, 9.1% of the deaths that occurred during the week ending March 19, 2022 (week 11), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.1% for this week. Among the 1,788 PIC deaths reported for this week, 928 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 17 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
No influenza-associated pediatric deaths were reported to CDC during week 11.
A total of 13 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: March 25, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
bump this
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated April 1, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 12, ending March 26, 2022
Influenza activity is still highest in the central and south-central regions of the country but appears to be declining slightly in these regions. Influenza activity is increasing in the northeast and northwest regions.
Viruses
Clinical Lab6.5%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.8%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 4 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET7.2 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,820
patients admitted to hospitals with influenza
this week.
NCHS Mortality8.3 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths1
influenza-associated death reported this week for a total of 14 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza activity is still highest the central and south-central parts of the country (Regions 6 and 7) but is beginning to decline. Influenza activity is increasing in the northeast and northwest regions (Regions 1, 2, and 10). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 9,010 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 486 (5.4%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 927 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 12, 1.8% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet is trending upward in four age groups (0-4 years, 5-24 years, 25-49 years and 50-64 years), while remaining stable among persons 65+ years.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 12, 102 (0.7%) of 13,961 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
A total of 2,122 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 26, 2022. The overall cumulative hospitalization rate was 7.2 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 12 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 12 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 52.5 to 96.1 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (19.5). Among adults aged 65 and older, rates were highest among adults aged 85 and older (38.9). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (10.3) followed by adults aged 50-64 years (6.7). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (10.3), followed by non-Hispanic Black persons (8.8).
Among 2,122 hospitalizations, 2,013 (94.9%) were associated with influenza A virus, 96 (4.5%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 9 (0.4%) with influenza virus for which the type was not determined. Among 537 hospitalizations with influenza A subtype information, 530 (98.7%) were A(H3N2), and 7 (1.3%) were A(H1N1)pdm09. Based on preliminary data, of the 2,122 laboratory-confirmed influenza-associated hospitalizations, 3.3% also tested positive for SARS-CoV-2.
Among 1,013 hospitalized adults with information on underlying medical conditions, 93% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 133 hospitalized children with information on underlying medical conditions, 75.9% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 12, 2,820 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 31, 2022, 8.3% of the deaths that occurred during the week ending March 26, 2022 (week 12), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.1% for this week. Among the 1,540 PIC deaths reported for this week, 750 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 27 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
One influenza-associated pediatric death occurring during the 2021-2022 season was reported to CDC during week 12. This death was associated with an influenza A(H3) virus and occurred during week 9 (the week ending March 5, 2022).
A total of 14 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 1, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated April 1, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 12, ending March 26, 2022
Influenza activity is still highest in the central and south-central regions of the country but appears to be declining slightly in these regions. Influenza activity is increasing in the northeast and northwest regions.
Viruses
Clinical Lab6.5%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.8%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 4 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET7.2 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,820
patients admitted to hospitals with influenza
this week.
NCHS Mortality8.3 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths1
influenza-associated death reported this week for a total of 14 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity is still highest in the central and south-central regions of the country but appears to be declining slightly in these regions. Influenza activity is increasing in the northeast and northwest regions.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness was stable this week compared with last week and remains below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past eight weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- One influenza-associated pediatric death was reported this week. There have been 14 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 3.5 million flu illnesses, 34,000 hospitalizations, and 2,000 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza activity is still highest the central and south-central parts of the country (Regions 6 and 7) but is beginning to decline. Influenza activity is increasing in the northeast and northwest regions (Regions 1, 2, and 10). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 9,010 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 486 (5.4%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 45,280 | 1,940,357 |
| No. of positive specimens (%) | 2,947 (6.5%) | 61,409 (3.2%) |
| Positive specimens by type | ||
| Influenza A | 2,924 (99.2%) | 60,149 (97.9%) |
| Influenza B | 23 (0.8%) | 1,260 (2.1%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 12,629 | 711,617 |
| No. of positive specimens | 339 | 15,812 |
| Positive specimens by type/subtype | ||
| Influenza A | 339 (100%) | 15,710 (99.4%) |
| (H1N1)pdm09 | 0 | 8 (0.1%) |
| H3N2 | 220 (100%) | 10,892 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 119 | 4,809 |
| Influenza B | 0 (0%) | 102 (0.6%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 0 | 68 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 927 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 4 | ||||
| 6B.1A | 4 (100%) | 5a.1 | 2 (50%) | ||
| 5a.2 | 2 (50%) | ||||
| A/H3 | 900 | ||||
| 3C.2a1b | 900 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 898 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
- A (H1N1)pdm09: Two A(H1N1)pdm09 viruses were antigenically characterized by HI, and 1 (50%) was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 1 (50%) was well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of 68 A(H3N2) viruses were antigenically characterized by HINT, and 3 (4%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 19 (28%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fourteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (79%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (79%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 941 | 4 | 914 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 941 | 4 | 914 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 941 | 4 | 914 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 911 | 4 | 884 | 23 | 0 |
| Reduced Susceptibility | 1 (0.1%) | (0.0%) | 1 (0.1%) | (0.0%) | (0.0%) |
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 12, 1.8% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet is trending upward in four age groups (0-4 years, 5-24 years, 25-49 years and 50-64 years), while remaining stable among persons 65+ years.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 12 (Week ending Mar. 26, 2022) | Week 11 (Week ending Mar. 19, 2022) | Week 12 (Week ending Mar. 26, 2022) | Week 11 (Week ending Mar. 19, 2022) | |
| Very High | 0 | 0 | 2 | 2 |
| High | 1 | 1 | 10 | 9 |
| Moderate | 4 | 4 | 16 | 17 |
| Low | 5 | 4 | 72 | 77 |
| Minimal | 43 | 44 | 558 | 561 |
| Insufficient Data | 2 | 2 | 271 | 263 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 12, 102 (0.7%) of 13,961 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
A total of 2,122 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and March 26, 2022. The overall cumulative hospitalization rate was 7.2 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 12 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 12 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 52.5 to 96.1 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (19.5). Among adults aged 65 and older, rates were highest among adults aged 85 and older (38.9). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (10.3) followed by adults aged 50-64 years (6.7). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (10.3), followed by non-Hispanic Black persons (8.8).
Among 2,122 hospitalizations, 2,013 (94.9%) were associated with influenza A virus, 96 (4.5%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 9 (0.4%) with influenza virus for which the type was not determined. Among 537 hospitalizations with influenza A subtype information, 530 (98.7%) were A(H3N2), and 7 (1.3%) were A(H1N1)pdm09. Based on preliminary data, of the 2,122 laboratory-confirmed influenza-associated hospitalizations, 3.3% also tested positive for SARS-CoV-2.
Among 1,013 hospitalized adults with information on underlying medical conditions, 93% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 133 hospitalized children with information on underlying medical conditions, 75.9% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 12, 2,820 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on March 31, 2022, 8.3% of the deaths that occurred during the week ending March 26, 2022 (week 12), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.1% for this week. Among the 1,540 PIC deaths reported for this week, 750 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 27 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
One influenza-associated pediatric death occurring during the 2021-2022 season was reported to CDC during week 12. This death was associated with an influenza A(H3) virus and occurred during week 9 (the week ending March 5, 2022).
A total of 14 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 1, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
bump this
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated April 8, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 13, ending April 2, 2022
Influenza activity increased nationally this week. Influenza activity is highest in the central and south-central regions of the country and is increasing in the northeastern regions.
Viruses
Clinical Lab8.3%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.9%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET8.0 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,965
patients admitted to hospitals with influenza
this week.
NCHS Mortality7.5 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths2
influenza-associated deaths reported this week for a total of 16 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza activity remains highest the central and south-central parts of the country (Regions 6 and 7). Influenza activity is increasing in the northeastern regions (Regions 1 and 2). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 9,303 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 489 (5.3%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 970 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 13, 1.9% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet has increased in one age group (5-24 years), while remaining stable in all other age groups (0-4 years, 25-49 years, 50-64 years, and 65+ years) compared to the previous week.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 13, 98 (0.7%) of 14,008 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
A total of 2,339 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 2, 2022. The overall cumulative hospitalization rate was 8.0 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 13 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 13 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 56.4 to 99.9 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (21.8). Among adults aged 65 and older, rates were highest among adults aged 85 and older (43.4). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (10.7) followed by adults aged 50-64 years (7.3). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (10.8), followed by non-Hispanic Black persons (9.6).
Among 2,339 hospitalizations, 2,225 (95.1%) were associated with influenza A virus, 99 (4.2%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 11 (0.5%) with influenza virus for which the type was not determined. Among 589 hospitalizations with influenza A subtype information, 582 (98.8%) were A(H3N2), and 7 (1.2%) were A(H1N1)pdm09. Based on preliminary data, of the 2,339 laboratory-confirmed influenza-associated hospitalizations, 3.2% also tested positive for SARS-CoV-2.
Among 1,114 hospitalized adults with information on underlying medical conditions, 93.1% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 166 hospitalized children with information on underlying medical conditions, 71.7% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 13, 2,965 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 7, 2022, 7.5% of the deaths that occurred during the week ending April 2, 2022 (week 13), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.0% for this week. Among the 1,297 PIC deaths reported for this week, 524 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 15 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 13. The deaths occurred in weeks 10 (the week ending March 12, 2022) and 13. Both deaths were associated with influenza A viruses for which no subtyping was performed.
A total of 16 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 8, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated April 8, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 13, ending April 2, 2022
Influenza activity increased nationally this week. Influenza activity is highest in the central and south-central regions of the country and is increasing in the northeastern regions.
Viruses
Clinical Lab8.3%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness1.9%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.
Long-term Care Facilities0.7%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET8.0 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations2,965
patients admitted to hospitals with influenza
this week.
NCHS Mortality7.5 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths2
influenza-associated deaths reported this week for a total of 16 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity increased nationally this week. Influenza activity is highest in the central and south-central regions of the country and is increasing in the northeastern regions.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness increased slightly this week compared with last week and remains below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past nine weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- Two influenza-associated pediatric deaths were reported this week. There have been 16 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 3.8 million flu illnesses, 38,000 hospitalizations, and 2,300 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Influenza activity remains highest the central and south-central parts of the country (Regions 6 and 7). Influenza activity is increasing in the northeastern regions (Regions 1 and 2). Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 9,303 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 489 (5.3%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 47,705 | 2,005,331 |
| No. of positive specimens (%) | 3,942 (8.3%) | 67,110 (3.3%) |
| Positive specimens by type | ||
| Influenza A | 3,883 (98.5%) | 65,775 (98.0%) |
| Influenza B | 59 (1.5%) | 1,335 (2.0%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 12,739 | 729,882 |
| No. of positive specimens | 422 | 16,538 |
| Positive specimens by type/subtype | ||
| Influenza A | 421 (99.8%) | 16,435 (99.4%) |
| (H1N1)pdm09 | 0 | 8 (0.1%) |
| H3N2 | 262 (100%) | 11,471 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 159 | 4,955 |
| Influenza B | 1 (0.2%) | 103 (0.6%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 1 | 69 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 970 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 4 | ||||
| 6B.1A | 4 (100%) | 5a.1 | 2 (50%) | ||
| 5a.2 | 2 (50%) | ||||
| A/H3 | 943 | ||||
| 3C.2a1b | 943 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 941 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Influenza A Viruses
- A (H1N1)pdm09: Three A(H1N1)pdm09 viruses were antigenically characterized by HI, and 2 (67%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 2 (67%) were well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of 68 A(H3N2) viruses were antigenically characterized by HINT, and 3 (4%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 19 (28%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fifteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (73%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (73%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 1,006 | 4 | 979 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 1,006 | 4 | 979 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 1,006 | 4 | 979 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 977 | 4 | 950 | 23 | 0 |
| Reduced Susceptibility | 1 (0.1%) | (0.0%) | 1 (0.1%) | (0.0%) | (0.0%) |
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 13, 1.9% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Nine of the 10 HHS regions are below their region-specific baselines; Region 7 is above its baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet has increased in one age group (5-24 years), while remaining stable in all other age groups (0-4 years, 25-49 years, 50-64 years, and 65+ years) compared to the previous week.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 13 (Week ending Apr. 2, 2022) | Week 12 (Week ending Mar. 26, 2022) | Week 13 (Week ending Apr. 2, 2022) | Week 12 (Week ending Mar. 26, 2022) | |
| Very High | 0 | 0 | 1 | 2 |
| High | 1 | 1 | 13 | 11 |
| Moderate | 3 | 3 | 13 | 18 |
| Low | 10 | 6 | 67 | 72 |
| Minimal | 41 | 44 | 565 | 565 |
| Insufficient Data | 0 | 1 | 270 | 261 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 13, 98 (0.7%) of 14,008 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
A total of 2,339 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 2, 2022. The overall cumulative hospitalization rate was 8.0 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 13 during the 2020-2021 season (0.7 per 100,000), but lower than the in-season rates observed in week 13 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 56.4 to 99.9 per 100,000 during the 2016-17 through 2019-20 seasons).
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (21.8). Among adults aged 65 and older, rates were highest among adults aged 85 and older (43.4). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (10.7) followed by adults aged 50-64 years (7.3). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (10.8), followed by non-Hispanic Black persons (9.6).
Among 2,339 hospitalizations, 2,225 (95.1%) were associated with influenza A virus, 99 (4.2%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 11 (0.5%) with influenza virus for which the type was not determined. Among 589 hospitalizations with influenza A subtype information, 582 (98.8%) were A(H3N2), and 7 (1.2%) were A(H1N1)pdm09. Based on preliminary data, of the 2,339 laboratory-confirmed influenza-associated hospitalizations, 3.2% also tested positive for SARS-CoV-2.
Among 1,114 hospitalized adults with information on underlying medical conditions, 93.1% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 166 hospitalized children with information on underlying medical conditions, 71.7% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 13, 2,965 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 7, 2022, 7.5% of the deaths that occurred during the week ending April 2, 2022 (week 13), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.0% for this week. Among the 1,297 PIC deaths reported for this week, 524 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 15 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 13. The deaths occurred in weeks 10 (the week ending March 12, 2022) and 13. Both deaths were associated with influenza A viruses for which no subtyping was performed.
A total of 16 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 8, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated April 15, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 14, ending April 9, 2022
Influenza activity increased nationally this week. Influenza activity is highest in the central and south-central regions of the country and is increasing in most regions.
Viruses
Clinical Lab8.4%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.0%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.
Long-term Care Facilities0.9%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET8.9 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations3,170
patients admitted to hospitals with influenza
this week.
NCHS Mortality7.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths3
influenza-associated deaths reported this week for a total of 19 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Influenza activity remains highest the central and south-central parts of the country (Regions 6 and 7). Influenza activity increased this week in most regions (Regions 1, 3, 4, 5, 7, and 9) compared with the previous week. Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 9,652 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 492 (5.1%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 1,020 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 14, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Seven of the 10 HHS regions are below their region-specific baselines; Regions 1, 2, and 7 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet has increased in two age groups (0-4 years and 5-24 years), while remaining stable in all other age groups (25-49 years, 50-64 years, and 65+ years) compared to the previous week.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 14, 126 (0.9%) of 14,167 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 2,628 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 9, 2022. The overall cumulative hospitalization rate was 8.9 per 100,000 population. This cumulative hospitalization rate is higher than the end-of-season cumulative hospitalization rates observed during the 2020-2021 (0.8 per 100,000) and 2011-2012 seasons (8.7 per 100,000), but lower than the in-season rates observed in week 14 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 59.4 to 101.6 per 100,000 during the 2016-17 through 2019-20 seasons). After peaking during the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined through the week ending February 19, 2022 (MMWR week 7), before increasing again through the week ending April 2, 2022 (MMWR week 13).
When examining cumulative rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (25.0). Among adults aged 65 and older, cumulative rates were highest among adults aged 85 and older (48.6). Among persons aged less than 65 years, cumulative rates per 100,000 population were highest among children aged 0-4 years (12.3) followed by adults aged 50-64 years (8.2).
Among 2,628 hospitalizations, 2,510 (95.5%) were associated with influenza A virus, 101 (3.8%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 13 (0.5%) with influenza virus for which the type was not determined. Among 649 hospitalizations with influenza A subtype information, 640 (98.6%) were A(H3N2), and 9 (1.4%) were A(H1N1)pdm09. Based on preliminary data, of the 2,628 laboratory-confirmed influenza-associated hospitalizations, 3.0% also tested positive for SARS-CoV-2.
Among 1,225 hospitalized adults with information on underlying medical conditions, 93.2% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 190 hospitalized children with information on underlying medical conditions, 71.6% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 14, 3,170 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 14, 2022, 7.1% of the deaths that occurred during the week ending April 9, 2022 (week 14), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.0% for this week. Among the 1,001 PIC deaths reported for this week, 367 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 19 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Three influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 14. The deaths occurred in weeks 7 (the week ending February 19, 2022), 12 (the week ending March 26, 2022), and 14 (the week ending April 9, 2022). All three deaths were associated with influenza A(H3) viruses.
A total of 19 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 15, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated April 15, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 14, ending April 9, 2022
Influenza activity increased nationally this week. Influenza activity is highest in the central and south-central regions of the country and is increasing in most regions.
Viruses
Clinical Lab8.4%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.0%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 1 jurisdiction experienced high or very high activity.
Long-term Care Facilities0.9%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET8.9 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations3,170
patients admitted to hospitals with influenza
this week.
NCHS Mortality7.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths3
influenza-associated deaths reported this week for a total of 19 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity increased nationally this week. Influenza activity is highest in the central and south-central regions of the country and is increasing in most regions.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness increased slightly this week compared with last week and remains below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past ten weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the end-of-seasons rates for the 2020-2021 and 2011-2012 seasons, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- Three influenza-associated pediatric deaths were reported this week. There have been 19 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 4.3 million flu illnesses, 42,000 hospitalizations, and 2,500 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- There are also prescription flu antiviral drugs that can be used to treat flu illness.
Influenza activity remains highest the central and south-central parts of the country (Regions 6 and 7). Influenza activity increased this week in most regions (Regions 1, 3, 4, 5, 7, and 9) compared with the previous week. Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 9,652 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 492 (5.1%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 46,198 | 2,063,495 |
| No. of positive specimens (%) | 3,902 (8.4%) | 71,966 (3.5%) |
| Positive specimens by type | ||
| Influenza A | 3,875 (99.3%) | 70,597 (98.1%) |
| Influenza B | 27 (0.7%) | 1,369 (1.9%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 11,262 | 742,000 |
| No. of positive specimens | 362 | 17,211 |
| Positive specimens by type/subtype | ||
| Influenza A | 362 (100%) | 17,108 (99.4%) |
| (H1N1)pdm09 | 0 | 8 (0.1%) |
| H3N2 | 264 (100%) | 12,096 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 98 | 5,003 |
| Influenza B | 0 (0%) | 103 (0.6%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 33 (97.1%) |
| Lineage not performed | 0 | 69 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 1,020 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 4 | ||||
| 6B.1A | 4 (100%) | 5a.1 | 2 (50%) | ||
| 5a.2 | 2 (50%) | ||||
| A/H3 | 993 | ||||
| 3C.2a1b | 993 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 991 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Influenza A Viruses
- A (H1N1)pdm09: Three A(H1N1)pdm09 viruses were antigenically characterized by HI, and 2 (67%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 2 (67%) were well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of 74 A(H3N2) viruses were antigenically characterized by HINT, and 4 (5%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 19 (26%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fifteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (73%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (73%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 1,034 | 4 | 1,007 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 1,034 | 4 | 1,007 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 1,034 | 4 | 1,007 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 1,016 | 4 | 989 | 23 | 0 |
| Reduced Susceptibility | 1 (0.1%) | (0.0%) | 1 (0.1%) | (0.0%) | (0.0%) |
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 14, 2.0% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This percentage is below the national baseline. Seven of the 10 HHS regions are below their region-specific baselines; Regions 1, 2, and 7 are above their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet has increased in two age groups (0-4 years and 5-24 years), while remaining stable in all other age groups (25-49 years, 50-64 years, and 65+ years) compared to the previous week.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 14 (Week ending Apr. 9, 2022) | Week 13 (Week ending Apr. 2, 2022) | Week 14 (Week ending Apr. 9, 2022) | Week 13 (Week ending Apr. 2, 2022) | |
| Very High | 0 | 0 | 1 | 2 |
| High | 1 | 1 | 7 | 14 |
| Moderate | 3 | 3 | 23 | 14 |
| Low | 10 | 11 | 79 | 70 |
| Minimal | 40 | 40 | 548 | 565 |
| Insufficient Data | 1 | 0 | 271 | 264 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 14, 126 (0.9%) of 14,167 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 2,628 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 9, 2022. The overall cumulative hospitalization rate was 8.9 per 100,000 population. This cumulative hospitalization rate is higher than the end-of-season cumulative hospitalization rates observed during the 2020-2021 (0.8 per 100,000) and 2011-2012 seasons (8.7 per 100,000), but lower than the in-season rates observed in week 14 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 59.4 to 101.6 per 100,000 during the 2016-17 through 2019-20 seasons). After peaking during the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined through the week ending February 19, 2022 (MMWR week 7), before increasing again through the week ending April 2, 2022 (MMWR week 13).
When examining cumulative rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (25.0). Among adults aged 65 and older, cumulative rates were highest among adults aged 85 and older (48.6). Among persons aged less than 65 years, cumulative rates per 100,000 population were highest among children aged 0-4 years (12.3) followed by adults aged 50-64 years (8.2).
Among 2,628 hospitalizations, 2,510 (95.5%) were associated with influenza A virus, 101 (3.8%) with influenza B virus, 4 (0.2%) with influenza A virus and influenza B virus co-infection, and 13 (0.5%) with influenza virus for which the type was not determined. Among 649 hospitalizations with influenza A subtype information, 640 (98.6%) were A(H3N2), and 9 (1.4%) were A(H1N1)pdm09. Based on preliminary data, of the 2,628 laboratory-confirmed influenza-associated hospitalizations, 3.0% also tested positive for SARS-CoV-2.
Among 1,225 hospitalized adults with information on underlying medical conditions, 93.2% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 190 hospitalized children with information on underlying medical conditions, 71.6% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 14, 3,170 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 14, 2022, 7.1% of the deaths that occurred during the week ending April 9, 2022 (week 14), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 7.0% for this week. Among the 1,001 PIC deaths reported for this week, 367 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 19 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Three influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 14. The deaths occurred in weeks 7 (the week ending February 19, 2022), 12 (the week ending March 26, 2022), and 14 (the week ending April 9, 2022). All three deaths were associated with influenza A(H3) viruses.
A total of 19 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 15, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
bump this
sharon sanders
Editor-in-Chief & President
Weekly U.S. Influenza Surveillance Report
Updated April 22, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 15, ending April 16, 2022
Influenza activity varies by region. Activity is highest in the northeast, south-central and mountain regions of the country.
Viruses
Clinical Lab8.9%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.1%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 3 jurisdiction experienced high or very high activity.
Long-term Care Facilities1.0%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET9.8 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations3,243
patients admitted to hospitals with influenza
this week.
NCHS Mortality7.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths3
influenza-associated deaths reported this week for a total of 22 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
Nationally, the percentage of specimens testing positive for influenza in clinical laboratories decreased slightly. However, activity varied by region; percent positivity increased this week in Regions 1, 2, 4, 8, and 10 compared with the previous week and decreased in Regions 3, 5, 6, 7, and 9. In Regions 1, 2, 6, and 8, more than 10% of specimens tested were positive for influenza. Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 10,011 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 496 (5.0%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 1,034 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) (H1N1pdm09, B/Victoria and B/Yamagata viruses) or neutralization-based HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2021-2022 Northern Hemisphere recommended egg-based and cell or recombinant-based vaccine viruses. Antigenic differences between viruses are determined by comparing how well the antibodies made against the vaccine reference viruses recognize the circulating viruses that have been grown in cell culture. Ferret antisera are useful because antibodies raised against a particular virus can often recognize small changes in the surface proteins of other viruses. In HI assays, viruses with similar antigenic properties have antibody titer differences of less than or equal to 4-fold when compared to the reference (vaccine) virus. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. Viruses selected for antigenic characterization are a subset representing the genetic changes in the surface proteins seen in genetically characterized viruses.
Influenza A Viruses
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 15, 2.1% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. Although this percentage is below the national baseline, ILI has been increasing steadily since mid-February. Seven of the 10 HHS regions are below their region-specific baselines; Regions 1 and 2 are above their respective baselines, while Region 7 is at baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet has increased in two age groups (0-4 years and 5-24 years), while remaining stable in all other age groups (25-49 years, 50-64 years, and 65+ years) compared to the previous week. The percentage of visits for respiratory illness has been increasing in all age groups since February (0-4 years, 5-24 years) and March (25-49 years, 50-64 years, and 65+ years).
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 15, 135 (1.0%) of 14,144 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 2,895 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 16, 2022. The overall cumulative hospitalization rate was 9.8 per 100,000 population. This cumulative hospitalization rate is higher than the end-of-season cumulative hospitalization rates observed during the 2020-2021 (0.8 per 100,000) and 2011-2012 seasons (8.7 per 100,000), but lower than the in-season rates observed in week 15 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 60.9 to 103.7 per 100,000 during the 2016-17 through 2019-20 seasons). After peaking during the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined through the week ending February 19, 2022 (MMWR week 7), before increasing again. The overall weekly rate observed during the week ending April 9, 2022 (MMWR week 14), was equal to the peak weekly rate observed during the week ending January 1, 2022.
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (27.6). Among adults aged 65 and older, rates were highest among adults aged 85 and older (54.1). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (13.3) followed by adults aged 50-64 years (9.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (15.2), followed by non-Hispanic Black persons (11.8).
Among 2,895 hospitalizations, 2,773 (95.8%) were associated with influenza A virus, 106 (3.7%) with influenza B virus, 4 (0.1%) with influenza A virus and influenza B virus co-infection, and 12 (0.4%) with influenza virus for which the type was not determined. Among 700 hospitalizations with influenza A subtype information, 691 (98.7%) were A(H3N2), and 9 (1.3%) were A(H1N1)pdm09. Based on preliminary data, of the 2,895 laboratory-confirmed influenza-associated hospitalizations, 2.8% also tested positive for SARS-CoV-2.
Among 1,399 hospitalized adults with information on underlying medical conditions, 93.5% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 212 hospitalized children with information on underlying medical conditions, 69.3% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
View Full Screen
Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 15, 3,243 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
View Chart Dataexcel icon | View Full Screen
Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 21, 2022, 7.1% of the deaths that occurred during the week ending April 16, 2022 (week 15), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.9% for this week. Among the 1,214 PIC deaths reported for this week, 427 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 37 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
View Chart Dataexcel icon | View Full Screen
Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Three influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 15. One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 3 (the week ending January 22, 2022). The two other deaths were associated with influenza A(H3) viruses and occurred during weeks 8 (the week ending February 26, 2022) and 11 (the week ending March 19, 2022).
A total of 22 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 22, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
Updated April 22, 2022
Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.
Key Updates for Week 15, ending April 16, 2022
Influenza activity varies by region. Activity is highest in the northeast, south-central and mountain regions of the country.
Viruses
Clinical Lab8.9%
positive for influenza
this week
Public Health Lab
The majority of viruses
detected are influenza A(H3N2).
Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness
Outpatient Respiratory Illness2.1%
of visits to a health care provider are for respiratory illness this week
(below baseline)
Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 3 jurisdiction experienced high or very high activity.
Long-term Care Facilities1.0%
of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease
FluSurv-NET9.8 per 100,000
cumulative hospitalization rate
HHS Protect Hospitalizations3,243
patients admitted to hospitals with influenza
this week.
NCHS Mortality7.1 %
of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)
Pediatric Deaths3
influenza-associated deaths reported this week for a total of 22 so far this season
All data are preliminary and may change as more reports are received.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.
Key Points
- Influenza activity varies by region. Activity is highest in the northeast, south-central and mountain regions of the country.
- The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
- The percentage of outpatient visits due to respiratory illness has steadily increased since mid-February but remains below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
- The number of hospital admissions reported to HHS Protect has increased each week for the past 11 weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the end-of-seasons rates for the 2020-2021 and 2011-2012 seasons, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
- Three influenza-associated pediatric deaths were reported this week. There have been 22 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 4.7 million flu illnesses, 47,000 hospitalizations, and 2,800 deaths from flu.
- An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
- There are also prescription flu antiviral drugs that can be used to treat flu illness.
Nationally, the percentage of specimens testing positive for influenza in clinical laboratories decreased slightly. However, activity varied by region; percent positivity increased this week in Regions 1, 2, 4, 8, and 10 compared with the previous week and decreased in Regions 3, 5, 6, 7, and 9. In Regions 1, 2, 6, and 8, more than 10% of specimens tested were positive for influenza. Influenza A(H3N2) viruses have been the most frequently detected influenza viruses this season. Of the 10,011 influenza positives reported this season by the public health labs and also tested for SARS-CoV-2, 496 (5.0%) were also positive for SARS-CoV-2. For regional and state level data and age group distribution, please visit FluView Interactive. Viruses known to be associated with recent live attenuated influenza vaccine (LAIV) receipt or found upon further testing to be a vaccine virus are not included as they are not circulating influenza viruses.
Clinical Laboratories
The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.
| No. of specimens tested | 45,179 | 2,128,423 |
| No. of positive specimens (%) | 4,014 (8.9%) | 78,342 (3.7%) |
| Positive specimens by type | ||
| Influenza A | 3,995 (99.5%) | 76,921 (98.2%) |
| Influenza B | 19 (0.5%) | 1,421 (1.8%) |
View Chart Data | View Full Screen Public Health Laboratories
The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.
| No. of specimens tested | 11,811 | 754,346 |
| No. of positive specimens | 442 | 17,938 |
| Positive specimens by type/subtype | ||
| Influenza A | 441 (99.8%) | 17,833 (99.4%) |
| (H1N1)pdm09 | 0 | 8 (0.1%) |
| H3N2 | 321 (100%) | 12,744 (99.9%) |
| H3N2v | 0 | 1 (<0.1%) |
| Subtyping not performed | 120 | 5,080 |
| Influenza B | 1 (0.2%) | 105 (0.6%) |
| Yamagata lineage | 0 | 1 (2.9%) |
| Victoria lineage | 0 | 34 (97.1%) |
| Lineage not performed | 1 | 70 |
View Chart Data | View Full Screen
Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data
Influenza Virus Characterization
CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories using the Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses representing viruses contained in the current influenza vaccines. The data are also used to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of circulating influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.
CDC has genetically characterized 1,034 influenza viruses collected since October 3, 2021. H3N2 viruses identified so far this season are genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.
| A/H1 | 4 | ||||
| 6B.1A | 4 (100%) | 5a.1 | 2 (50%) | ||
| 5a.2 | 2 (50%) | ||||
| A/H3 | 1,007 | ||||
| 3C.2a1b | 1,007 (100%) | 1a | 1 (0.1%) | ||
| 1b | 1 (0.1%) | ||||
| 2a | 0 | ||||
| 2a.1 | 0 | ||||
| 2a.2 | 1,005 (99.8%) | ||||
| 3C.3a | 0 | 3a | 0 | ||
| B/Victoria | 23 | ||||
| V1A | 23 (100%) | V1A | 0 | ||
| V1A.1 | 0 | ||||
| V1A.3 | 9 (39.1%) | ||||
| V1A.3a | 0 | ||||
| V1A.3a.1 | 0 | ||||
| V1A.3a.2 | 14 (60.9%) | ||||
| B/Yamagata | 0 | ||||
| Y3 | 0 |
Influenza A Viruses
- A (H1N1)pdm09: Three A(H1N1)pdm09 viruses were antigenically characterized by HI, and 2 (67%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/588/2019-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines and 2 (67%) were well recognized by ferret antisera to egg-grown A/Victoria/2570/2019-like reference viruses representing the A(H1N1)pdm09 component for the egg-based influenza vaccines.
- A (H3N2): A subset of 83 A(H3N2) viruses were antigenically characterized by HINT, and 4 (5%) were well recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 19 (23%) were well recognized by ferret antisera to egg-grown A/Cambodia/E0826360/2020-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.
- B/Victoria: Fifteen B/Victoria lineage viruses were antigenically characterized by HI, and 11 (73%) were well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and 11 (73%) were well recognized by ferret antisera to egg-grown B/Washington/02/2019-like reference viruses representing the B/Victoria component for egg-based influenza vaccines.
- B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.
CDC assesses susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the United States since October 3, 2021, were tested for antiviral susceptibility as follows:
| Neuraminidase Inhibitors | |||||||
| Oseltamivir | Viruses Tested | 1,121 | 5 | 1,093 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Peramivir | Viruses Tested | 1,121 | 5 | 1,093 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Zanamivir | Viruses Tested | 1,121 | 5 | 1,093 | 23 | 0 | |
| Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| Highly Reduced Inhibition | (0.0%) | (0.0%) | (0.0%) | (0.0%) | (0.0%) | ||
| PA Cap-Dependent Endonuclease Inhibitor | Baloxavir | Viruses Tested | 1,093 | 5 | 1,065 | 23 | 0 |
| Reduced Susceptibility | 1 (0.1%) | (0.0%) | 1 (0.1%) | (0.0%) | (0.0%) |
One A(H3N2) virus had a PA-I38M amino acid substitution previously associated with reduced baloxavir susceptibility and showed ~8-fold reduced susceptibility to baloxavir in vitro.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms, including influenza, SARS-CoV-2, and RSV. Due to the COVID-19 pandemic, health care-seeking behaviors have changed, and people may be accessing the health care system in alternative settings not captured as a part of ILINet or at a different point in their illness than they might have before the pandemic. Therefore, it is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity. CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
Outpatient Respiratory Illness Visits
Nationwide during week 15, 2.1% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. Although this percentage is below the national baseline, ILI has been increasing steadily since mid-February. Seven of the 10 HHS regions are below their region-specific baselines; Regions 1 and 2 are above their respective baselines, while Region 7 is at baseline. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data (current season only) | View Full ScreenOutpatient Respiratory Illness Visits by Age Group
More than 70% of ILINet participants provide both the number of patient visits for respiratory illness and the total number of patient visits for the week broken out by age group. Data from this subset of providers are used to calculate the percentages of patient visits for respiratory illness by age group.
The percentage of visits for respiratory illness reported in ILINet has increased in two age groups (0-4 years and 5-24 years), while remaining stable in all other age groups (25-49 years, 50-64 years, and 65+ years) compared to the previous week. The percentage of visits for respiratory illness has been increasing in all age groups since February (0-4 years, 5-24 years) and March (25-49 years, 50-64 years, and 65+ years).
* Effective October 3, 2021 (week 40), the ILI definition (fever plus cough or sore throat) no longer includes “without a known cause other than influenza.”
View Chart Data | View Full Screen
Outpatient Respiratory Illness Activity Map
Data collected in ILINet are used to produce a measure of ILI activity* by state/jurisdiction and Core Based Statistical Areas (CBSA).
| Week 15 (Week ending Apr. 16, 2022) | Week 14 (Week ending Apr. 9, 2022) | Week 15 (Week ending Apr. 16, 2022) | Week 14 (Week ending Apr. 9, 2022) | |
| Very High | 0 | 0 | 2 | 2 |
| High | 3 | 2 | 10 | 7 |
| Moderate | 2 | 2 | 24 | 26 |
| Low | 10 | 11 | 84 | 76 |
| Minimal | 39 | 40 | 536 | 555 |
| Insufficient Data | 1 | 0 | 273 | 263 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of influenza activity for the entire jurisdiction or CBSA. Differences in the data presented here by CDC and independently by some health departments likely represent differing levels of data completeness with data presented by the health department likely being the more complete.
Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map
Long-term Care Facility (LTCF) Surveillance
LTCFs (e.g., nursing homes/skilled nursing, long-term care for the developmentally disabled, and assisted living facilities) from all 50 states and U.S. territories report data on influenza virus infections among residents through the National Healthcare Safety Network (NHSN) Long-term Care Facility Component. During week 15, 135 (1.0%) of 14,144 reporting LTCFs reported at least one influenza positive test among their residents.
View Chart Dataexcel icon | View Full Screen
Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Dataexternal icon
Hospitalization Surveillance
FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET hospitalization data are preliminary. As data are received each week, prior case counts and rates are updated accordingly.
A total of 2,895 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and April 16, 2022. The overall cumulative hospitalization rate was 9.8 per 100,000 population. This cumulative hospitalization rate is higher than the end-of-season cumulative hospitalization rates observed during the 2020-2021 (0.8 per 100,000) and 2011-2012 seasons (8.7 per 100,000), but lower than the in-season rates observed in week 15 during the 4 seasons preceding the COVID-19 pandemic (these ranged from 60.9 to 103.7 per 100,000 during the 2016-17 through 2019-20 seasons). After peaking during the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined through the week ending February 19, 2022 (MMWR week 7), before increasing again. The overall weekly rate observed during the week ending April 9, 2022 (MMWR week 14), was equal to the peak weekly rate observed during the week ending January 1, 2022.
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (27.6). Among adults aged 65 and older, rates were highest among adults aged 85 and older (54.1). Among persons aged less than 65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (13.3) followed by adults aged 50-64 years (9.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic American Indian or Alaska Native persons (15.2), followed by non-Hispanic Black persons (11.8).
Among 2,895 hospitalizations, 2,773 (95.8%) were associated with influenza A virus, 106 (3.7%) with influenza B virus, 4 (0.1%) with influenza A virus and influenza B virus co-infection, and 12 (0.4%) with influenza virus for which the type was not determined. Among 700 hospitalizations with influenza A subtype information, 691 (98.7%) were A(H3N2), and 9 (1.3%) were A(H1N1)pdm09. Based on preliminary data, of the 2,895 laboratory-confirmed influenza-associated hospitalizations, 2.8% also tested positive for SARS-CoV-2.
Among 1,399 hospitalized adults with information on underlying medical conditions, 93.5% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 212 hospitalized children with information on underlying medical conditions, 69.3% had at least one reported underlying medical condition; the most commonly reported condition was asthma.
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Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods |FluView Interactive: Rates by Age, Sex, and Race/Ethnicity or Data on Patient Characteristics
FluSurv-Net data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations, and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden...-estimates.htm
HHS Protect Hospitalization Surveillance
Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 15, 3,243 patients with laboratory-confirmed influenza were admitted to the hospital.
Effective February 2, 2022, hospitals are required to report laboratory-confirmed influenza hospitalizations to HHS Protect daily. Prior to this update, reporting influenza hospitalizations was optional. See COVID-19 Guidance for Hospital Reporting and FAQspdf iconexternal icon for additional details on this guidance.
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Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Dataexternal icon
Mortality Surveillance
National Center for Health Statistics (NCHS) Mortality Surveillance
Based on NCHS mortality surveillance data available on April 21, 2022, 7.1% of the deaths that occurred during the week ending April 16, 2022 (week 15), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.9% for this week. Among the 1,214 PIC deaths reported for this week, 427 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 37 listed influenza, indicating that current PIC mortality is due primarily to COVID-19 and not influenza. The data presented are preliminary and may change as more data are received and processed.
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Additional pneumonia, influenza and COVID-19 mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Influenza-Associated Pediatric Mortality
Three influenza-associated pediatric deaths occurring during the 2021-2022 season were reported to CDC during week 15. One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 3 (the week ending January 22, 2022). The two other deaths were associated with influenza A(H3) viruses and occurred during weeks 8 (the week ending February 26, 2022) and 11 (the week ending March 19, 2022).
A total of 22 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC.
View Full Screen Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive
Additional National and International Influenza Surveillance Information
FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics.
National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH.
U.S. State and local influenza surveillance: Select a jurisdiction below to access the latest local influenza information.
Additional influenza surveillance information from participating WHO member nations is available through
FluNetexternal icon and the Global Epidemiology Reports.external icon
WHO Collaborating Centers for Influenza:
Australiaexternal icon, Chinaexternal icon, Japanexternal icon, the United Kingdomexternal icon, and the United States (CDC in Atlanta, Georgia)
Europe:
The most up-to-date influenza information from Europe is available from WHO/Europe and the European Centre for Disease Prevention and Controlexternal icon.
Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch reportexternal icon.
Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health Englandexternal icon.
Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.
A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.
Page last reviewed: April 22, 2022, 11:00 AM
https://www.cdc.gov/flu/weekly/index.htm
sharon sanders
Editor-in-Chief & President
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