Announcement

**Lance** · October 14, 2022, 04:35 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated October 14, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 40, ending October 8, 2022

Early increases in seasonal influenza activity have been reported in most of the United States, with the southeast and south-central areas of the country reporting the highest levels of activity.
Viruses

Clinical Lab3.3%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Influenza virus characterization information will be reported later this season.
Illness

Outpatient Respiratory Illness2.6%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 6 jurisdictions experienced high or very high activity.

Long-term Care Facilities0.3%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET
Hospitalization rates will be updated starting later this season.

HHS Protect Hospitalizations1,322

patients admitted to hospitals with influenza
this week.

NCHS Mortality8.7%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)

Pediatric Deaths3

influenza-associated deaths reported this week; all occurred during the 2021-2022 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

This is the first FluView of the 2022-2023 influenza season.
Influenza activity is low but increasing in most of the country. Regions 4 (southeast) and 6 (south-central) are reporting the highest levels of flu activity.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine, ideally by the end of October.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing; however, activity varies by region. Percent positivity increased this week in regions 3, 4, 6, 7, and 9, and was similar to or lower than the previous week in all other regions. 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	58,481	53,565
No. of positive specimens (%)	1,274 (2.2%)	1,766 (3.3%)
*Positive specimens by type*
Influenza A	1,213 (95.2%)	1,686 (95.5%)
Influenza B	61 (4.8%)	80 (4.5%)

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	7,729	7,261
No. of positive specimens	133	83
*Positive specimens by type/subtype*
Influenza A	130 (97.7%)	81 (97.6%)
(H1N1)pdm09	18 (26.9%)	16 (36.4%)
H3N2	49 (73.1%)	28 (63.6%)
H3N2v	0	0
Subtyping not performed	63	37
Influenza B	3 (2.3%)	2 (2.4%)
Yamagata lineage	0	0
Victoria lineage	1 (100%)	1 (100%)
Lineage not performed	2	1

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 according to 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 396 influenza viruses collected since May 1, 2022. While there are little data to date, most of the H3N2 viruses so far are genetically closely related to the 2022-2023 Northern Hemisphere vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses have continued to evolve.

A/H1	21
		6B.1A	21 (100%)	5a.1	5 (23.8%)
				5a.2	16 (76.2%)
A/H3	373
		3C.2a1b	373 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	373 (100%)
		3C.3a	0	3a	0
B/Victoria	2
		V1A	2 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	2 (100%)
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 2022-2023 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 none 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 or 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): Twenty-four A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 22 (92%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: No influenza B/Victoria-lineage viruses were antigenically characterized by HI.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

Virus antiviral susceptibility data will be reported later this season when a sufficient number of specimens have been tested.
Outpatient Respiratory Illness Surveillance

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as 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 40, 2.6% 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 increased compared to week 39 and is above the national baseline of 2.5%. Eight of the 10 HHS regions are below their region-specific baselines; regions 3 and 4 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 is trending upward in 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 40 (Week ending Oct. 8, 2022)	Week 39 (Week ending Oct. 1, 2022)	Week 40 (Week ending Oct. 8, 2022)	Week 39 (Week ending Oct. 1, 2022)
Very High	1	0	7	4
High	5	4	24	25
Moderate	3	2	36	36
Low	14	11	106	92
Minimal	32	38	490	507
Insufficient Data	0	0	266	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 40, 41 (0.3%) of 14,331 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
Hospitalization Surveillance

FluSurv-NET

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in selected counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET estimated hospitalization rates will be updated weekly starting later this season.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 40, 1,322 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on October 13, 2022, 8.7% of the deaths that occurred during the week ending October 8, 2022 (week 40), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 5.8% for this week. Among the 1,928 PIC deaths reported for this week, 898 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and nine 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 Data | 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 40. The deaths were associated with influenza A (H3) viruses and occurred during weeks 5, 16, and 21 of 2022 (weeks ending February 5, April 23, and May 28 respectively).

A total of 43 influenza-associated pediatric deaths occurring during the 2021-2022 season have been reported to CDC. No influenza-associated pediatric deaths occurring during the 2022-2023 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · October 21, 2022, 05:42 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated October 21, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 41, ending October 15, 2022

Early increases in seasonal influenza activity have been reported in most of the United States, with the southeast and south-central areas of the country reporting the highest levels of activity.
Viruses

Clinical Lab4.4%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization are summarized in this report.
Illness

Outpatient Respiratory Illness3.0%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 8 jurisdictions experienced moderate activity and 10 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-NET
Hospitalization rates will be updated starting later this season.

HHS Protect Hospitalizations1,674

patients admitted to hospitals with influenza
this week.

NCHS Mortality8.8%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)

Pediatric Deaths0

influenza-associated deaths reported this week

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. Regions 4 (southeast) and 6 (south-central) are reporting the highest levels of flu activity.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine, ideally by the end of October.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing; however, activity varies by region. Percent positivity increased ≥ 0.5% this week in regions 3, 4, 6, and 9, and was similar to or lower than the previous week in all other regions. 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	61,813	134,628
No. of positive specimens (%)	2,712 (4.4%)	4,782 (3.6%)
*Positive specimens by type*
Influenza A	2,639 (97.3%)	4,610 (96.4%)
Influenza B	73 (2.7%)	172 (3.6%)

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	6,854	14,607
No. of positive specimens	137	349
*Positive specimens by type/subtype*
Influenza A	135 (98.5%)	341 (97.7%)
(H1N1)pdm09	20 (22.5%)	50 (20.5%)
H3N2	69 (77.5%)	194 (79.5%)
H3N2v	0	0
Subtyping not performed	46	97
Influenza B	2 (1.5%)	8 (2.3%)
Yamagata lineage	0	0
Victoria lineage	0	2 (100%)
Lineage not performed	2	6

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

A human infection with a novel influenza A virus was reported by the Michigan Department of Health and Human Services. The patient was infected with an influenza A(H3N2) variant (A(H3N2)v) virus. The illness occurred during week 36 of 2022. The patient is <18 years of age, was not hospitalized, and has recovered from their illness. An investigation by local public health officials found that the patient had indirect swine exposure at an agricultural fair prior to their illness onset. Additional investigation did not identify respiratory illness in any of the patient’s household contacts. No person-to-person transmission of A(H3N2)v virus associated with this patient has been identified.

A total of nine human infections with variant novel influenza A viruses have been reported in the United States in 2022, including four H3N2v (Michigan (1) West Virginia (3)) and five H1N2v (Georgia, Michigan, Ohio, Oregon, Wisconsin) viruses. 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 exposure to swine, but human-to-human transmission can occur. It is important to note that 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 understood, and appropriate public health measures can be taken.

Additional information on influenza in swine, variant influenza virus infection in humans, and guidance 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:

Surveillance Methods | FluView Interactive

Influenza Virus Characterization

CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local public health laboratories according to 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 genetically characterized 446 influenza viruses collected since May 1, 2022.

A/H1	36
		6B.1A	36 (100%)	5a.1	5 (13.9%)
				5a.2	31 (86.1%)
A/H3	408
		3C.2a1b	408 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	408 (100%)
		3C.3a	0	3a	0
B/Victoria	2
		V1A	2 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	2 (100%)
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 2022-2023 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: Eleven A(H1N1)pdm09 viruses were antigenically characterized by HI, and 9 (82%) 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 9 (82%) 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): Thirty-two A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 30 (94%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

Virus antiviral susceptibility data will be reported later this season when a sufficient number of specimens have been tested.
Outpatient Respiratory Illness Surveillance

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as 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 41, 3.0% 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 increased compared to week 40 and is above the national baseline of 2.5%. Regions 2, 3, 4, and 6 are above their region-specific baselines, and regions 7 and 9 are at their respective baselines. The remaining four 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 is trending upwards in 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 41 (Week ending Oct. 15, 2022)	Week 40 (Week ending Oct. 8, 2022)	Week 41 (Week ending Oct. 15, 2022)	Week 40 (Week ending Oct. 8, 2022)
Very High	1	1	9	9
High	9	4	38	23
Moderate	8	4	60	38
Low	9	14	101	106
Minimal	28	32	389	495
Insufficient Data	0	0	332	258

*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 41, 64 (0.4%) of 14,239 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
Hospitalization Surveillance

FluSurv-NET

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in selected counties in 14 states and represents approximately 9% of the U.S. population. FluSurv-NET estimated hospitalization rates will be updated weekly starting later this season.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 41, 1,674 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on October 20, 2022, 8.8% of the deaths that occurred during the week ending October 15, 2022 (week 41), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 5.8% for this week. Among the 2,060 PIC deaths reported for this week, 931 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 Data | 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 41. No influenza-associated pediatric deaths occurring during the 2022-2023 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · October 28, 2022, 04:24 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated October 28, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 42, ending October 22, 2022

Early increases in seasonal influenza activity continue, with the southeast and south-central areas of the country reporting the highest levels of activity.
Viruses

Clinical Lab6.2%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization are summarized in this report.
Illness

Outpatient Respiratory Illness3.3%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 1 jurisdiction experienced moderate activity and 13 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-NET1.5 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations2,332

patients admitted to hospitals with influenza
this week.

NCHS Mortality9.2%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)

Pediatric Deaths1

influenza-associated death reported this week

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 continues to increase. Regions 4 (southeast) and 6 (south-central) are reporting the highest levels of flu activity.
The first influenza-associated pediatric death of the 2022-2023 season was reported this week.
CDC estimates that, so far this season, there have been at least 880,000 flu illnesses, 6,900 hospitalizations, and 360 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 42 during previous seasons going back to 2010-2011.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing; however, activity varies by region. Percent positivity increased ≥ 0.5% this week in regions 2, 3, 4, 5, 6, 7, 8, 9, and 10, and was similar to the previous week but trending upward in region 1. 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	66,955	216,088
No. of positive specimens (%)	4,129 (6.2%)	9,142 (4.2%)
*Positive specimens by type*
Influenza A	4,061 (98.4%)	8,887 (97.2%)
Influenza B	68 (1.6%)	255 (2.8%)

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	8,367	24,935
No. of positive specimens	298	984
*Positive specimens by type/subtype*
Influenza A	291 (97.7%)	965 (98.1%)
(H1N1)pdm09	43 (25.4%)	121 (16.3%)
H3N2	126 (74.6%)	621 (83.7%)
H3N2v	0	0
Subtyping not performed	122	223
Influenza B	7 (2.3%)	19 (1.9%)
Yamagata lineage	0	0
Victoria lineage	0	8 (100%)
Lineage not performed	7	11

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 according to 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 genetically characterized 452 influenza viruses collected since May 1, 2022.

A/H1	38
		6B.1A	38 (100%)	5a.1	5 (13.2%)
				5a.2	33 (86.8%)
A/H3	412
		3C.2a1b	412 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	412 (100%)
		3C.3a	0	3a	0
B/Victoria	2
		V1A	2 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	2 (100%)
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 2022-2023 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: Fourteen A(H1N1)pdm09 viruses were antigenically characterized by HI, and 12 (86%) 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 12 (86%) 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): Thirty-five A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 33 (94%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

Virus antiviral susceptibility data will be reported later this season when a sufficient number of specimens have been tested.
Outpatient Respiratory Illness Surveillance

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as 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 42, 3.3% 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 increased compared to week 41 and is above the national baseline of 2.5%. Regions 2, 3, 4, 5, 6, 7, and 9 are at or above their region-specific baselines. The remaining three 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 Screen
Outpatient 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 upwards in 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 42 (Week ending Oct. 22, 2022)	Week 41 (Week ending Oct. 15, 2022)	Week 42 (Week ending Oct. 22, 2022)	Week 41 (Week ending Oct. 15, 2022)
Very High	2	1	13	9
High	11	9	65	39
Moderate	1	8	63	63
Low	14	8	134	103
Minimal	26	29	398	414
Insufficient Data	1	0	256	301

*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 42, 75 (0.5%) of 14,264 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 443 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and October 22, 2022; 94.4% were associated with influenza A virus, 3.4% were associated with influenza B virus, 0.5% with influenza A virus and influenza B virus co-infection, and 1.8% with influenza virus for which the type was not determined. Among 59 hospitalizations with influenza A subtype information, 27.1% were A(H1N1)pdm09 virus and 72.9% were A(H3N2).

The overall cumulative hospitalization rate per 100,000 population was 1.5. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 42 during previous seasons going back to 2010-2011, which ranged from 0 to 0.3. The highest hospitalization rates per 100,000 population were among adults aged ≥ 65 years (3.0) and children aged 0-4 years (3.0), followed by children aged 5-17 years (1.7), adults aged 50-64 (1.3) and adults aged 18-49 years (0.8).

Cumulative hospitalization rates for each age group were higher than cumulative in-season hospitalization rates previously observed during week 42; since 2010-11, in-season rates ranged from 0 to 0.4 among children 0-4 years, 0 to 0.1 among children 5-17 years, 0 to 0.2 among adults 18-49 years, 0 to 0.3 among adults 50-64 years, and 0 to 1.0 among adults ≥ 65 years.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 42, 2,332 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on October 27, 2022, 9.2% of the deaths that occurred during the week ending October 22, 2022 (week 42), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 5.9% for this week. Among the 2,128 PIC deaths reported for this week, 949 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 Data | 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 2022-2023 season was reported to CDC during week 42. The death was associated with an influenza A(H3) virus and occurred during week 40 (the week ending October 8, 2022). This is the first influenza-associated pediatric death occurring during the 2022-2023 season that has 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · November 4, 2022, 12:49 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated November 4, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 43, ending October 29, 2022

Early increases in seasonal influenza activity continue nationwide. The southeastern and south-central areas of the country are reporting the highest levels of activity followed by the Mid-Atlantic and the south-central West Coast regions.
Viruses

Clinical Lab9.0%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization are summarized in this report.
Illness

Outpatient Respiratory Illness4.3%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 4 jurisdictions experienced moderate activity and 19 jurisdictions experienced high or very high activity.

Long-term Care Facilities0.8%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET2.9 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations4,326

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 Deaths2

deaths were reported (1 occurred in 2021-22 season and 1 occurred in 2022-23 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 continues to increase. Regions 4 (Southeast) and 6 (South-Central) are reporting the highest levels of flu activity, followed by regions 3 (Mid-Atlantic) and 9 (south-central West Coast).
One human infection with a novel influenza A virus was reported by the New Mexico Department of Health.
The second pediatric death of the 2022-23 influenza season was reported this week.
CDC estimates that, so far this season, there have been at least 1,600,000 illnesses, 13,000 hospitalizations, and 730 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 43 during every previous season since 2010-2011.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing. Percent positivity increased ≥ 0.5 percentage points this week in all regions. The majority of viruses detected so far this season have been influenza A(H3N2), however the proportion of influenza A(H1N1) viruses is increasing nationally. In Region 5, the majority of viruses detected during week 43 were influenza A(H1N1). 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	83,742	327,191
No. of positive specimens (%)	7,504 (9.0%)	17,271 (5.3%)
*Positive specimens by type*
Influenza A	7,422 (98.9%)	16,901 (97.9%)
Influenza B	82 (1.1%)	370 (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	8,187	33,638
No. of positive specimens	467	1,699
*Positive specimens by type/subtype*
Influenza A	466 (99.8%)	1,674 (98.5%)
(H1N1)pdm09	108 (33.8%)	289 (20.9%)
H3N2	212 (66.3%)	1,097 (79.1%)
H3N2v	0	0
Subtyping not performed	146	288
Influenza B	1 (0.2%)	25 (1.5%)
Yamagata lineage	0	1 (6.3%)
Victoria lineage	0	15 (93.8%)
Lineage not performed	1	9

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
Public Health Novel Influenza A Virus

A human infection with a novel influenza A virus was reported by the New Mexico Department of Health. The patient was infected with an influenza A(H3N2) variant (A(H3N2)v) virus. The illness occurred during the week ending October 15, 2022 (week 41). The patient is <18 years of age and is recovering from their illness. An investigation by local public health officials found that the patient had swine exposure prior to their illness onset. No person-to-person transmission of A(H3N2)v virus associated with this patient has been identified. The investigation is ongoing.

A total of ten human infections with variant novel influenza A viruses have been reported in the United States in 2022, including five H3N2v (Michigan, New Mexico, West Virginia (3)) and five H1N2v (Georgia, Michigan, Ohio, Oregon, Wisconsin) viruses. 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 exposure to swine, but human-to-human transmission can occur. It is important to note that 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 understood, and appropriate public health measures can be taken.

Additional information on influenza in swine, variant influenza virus infection in humans, and guidance to interact safely with swine can be found at www.cdc.gov/flu/swineflu/index.htm.

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 according to 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 genetically characterized 460 influenza viruses collected since May 1, 2022.

A/H1	40
		6B.1A	40 (100%)	5a.1	5 (12.5%)
				5a.2	35 (87.5%)
A/H3	418
		3C.2a1b	418 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	418 (100%)
		3C.3a	0	3a	0
B/Victoria	2
		V1A	2 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	2 (100%)
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 2022-2023 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: Twenty-six A(H1N1)pdm09 viruses were antigenically characterized by HI, and 24 (92%) 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 24 (92%) 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): Forty-two A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 40 (95%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

Virus antiviral susceptibility data will be reported later this season when a sufficient number of specimens have been tested.
Outpatient Respiratory Illness Surveillance

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as 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 43, 4.3% 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 is an increase compared to week 42 and is above the national baseline of 2.5%. Regions 1, 2, 3, 4, 5, 6, 7, and 9 are above their region-specific baselines. The remaining two 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 Screen
Outpatient 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 increasing in all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years).

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 43 (Week ending Oct. 29, 2022)	Week 42 (Week ending Oct. 22, 2022)	Week 43 (Week ending Oct. 29, 2022)	Week 42 (Week ending Oct. 22, 2022)
Very High	11	1	42	9
High	8	4	97	24
Moderate	4	4	82	38
Low	11	12	131	109
Minimal	21	34	332	505
Insufficient Data	0	0	245	244

*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 43, 117 (0.8%) of 14,221 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 842 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and October 29, 2022; 95.0% were associated with influenza A virus, 3.6% were associated with influenza B virus, 0.5% with influenza A virus and influenza B virus co-infection, and 1.0% with influenza virus for which the type was not determined. Among 115 hospitalizations with influenza A subtype information, 26.1% were A(H1N1)pdm09 virus and 72.2% were A(H3N2).

The overall cumulative hospitalization rate per 100,000 population was 2.9. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 43 during previous seasons going back to 2010-2011, which ranged from 0 to 0.5. The highest hospitalization rates per 100,000 population were among adults aged ≥ 65 years (6.3), followed by children aged 0-4 years (5.5), adults aged 50-64 (2.8), children aged 5-17 years (2.6), and adults aged 18-49 years (1.5).

Cumulative hospitalization rates for each age group were higher than cumulative in-season hospitalization rates previously observed during week 43; since 2010-11, in-season rates ranged from 0 to 0.9 among children 0-4 years, 0 to 0.3 among children 5-17 years, 0 to 0.2 among adults 18-49 years, 0 to 0.5 among adults 50-64 years, and 0.1 to 1.4 among adults ≥ 65 years.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 43, 4,326 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on November 3, 2022, 9.1% of the deaths that occurred during the week ending October 29, 2022 (week 43), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.0% for this week. Among the 2,153 PIC deaths reported for this week, 988 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 29 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 Data | 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 were reported to CDC during week 43. Both deaths were associated with influenza A(H3) viruses.

One death occurred during week 43 (the week ending October 29, 2022). This was the second influenza-associated pediatric death occurring during the 2022-2023 season that has been reported to CDC.

The other death occurred during week 37 (the week ending September 17, 2022), which was during the 2021-2022 season. The total number of pediatric deaths that occurred in the 2021-2022 season is 44.

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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · November 11, 2022, 09:28 AM

Weekly U.S. Influenza Surveillance Report

Print
Updated November 10, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 44, ending November 5, 2022

Early increases in seasonal influenza activity continue nationwide. The southeastern and south-central areas of the country are reporting the highest levels of activity followed by the Mid-Atlantic and the south-central West Coast regions.
Viruses

Clinical Lab12.8%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization are summarized in this report.
Illness

Outpatient Respiratory Illness5.5%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 6 jurisdictions experienced moderate activity and 25 jurisdictions 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-NET5.0 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations6,465

patients admitted to hospitals with influenza
this week.

NCHS Mortality9.0%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)

Pediatric Deaths3

deaths were reported this week for 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 continues to increase. Regions 4 (Southeast) and 6 (South-Central) are reporting the highest levels of flu activity, followed by regions 3 (Mid-Atlantic) and 9 (south-central West Coast).
Three influenza-associated pediatric deaths were reported this week.
CDC estimates that, so far this season, there have been at least 2.8 million illnesses, 23,000 hospitalizations, and 1,300 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 44 during every previous season since 2010-2011.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing. Percent positivity increased ≥ 0.5 percentage points this week in all regions. The majority of viruses detected so far this season have been influenza A(H3N2), however approximately 30% of the subtyped influenza A viruses have been influenza A(H1N1) viruses. 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	103,311	457,029
No. of positive specimens (%)	13,178 (12.8%)	32,046 (7.0%)
*Positive specimens by type*
Influenza A	13,086 (99.3%)	31,558 (98.5%)
Influenza B	92 (0.7%)	488 (1.5%)

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	8,824	44,656
No. of positive specimens	705	2,854
*Positive specimens by type/subtype*
Influenza A	700 (99.3%)	2,824 (98.9%)
(H1N1)pdm09	108 (24.9%)	485 (21.2%)
H3N2	325 (75.1%)	1,798 (78.8%)
H3N2v	0	0
Subtyping not performed	267	541
Influenza B	5 (0.7%)	30 (1.1%)
Yamagata lineage	0	0
Victoria lineage	0	15 (100.0%)
Lineage not performed	5	15

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 according to 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 genetically characterized 490 influenza viruses collected since May 1, 2022.

A/H1	57
		6B.1A	57 (100%)	5a.1	5 (8.8%)
				5a.2	52 (91.2%)
A/H3	431
		3C.2a1b	431 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	431 (100%)
		3C.3a	0	3a	0
B/Victoria	2
		V1A	2 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	2 (100%)
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 2022-2023 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:Twenty-six A(H1N1)pdm09 viruses were antigenically characterized by HI, and 24 (92%) 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 24 (92%) 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): Forty-two A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 40 (95%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

Virus antiviral susceptibility data will be reported later this season when a sufficient number of specimens have been tested.
Outpatient Respiratory Illness Surveillance

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as 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 44, 5.5% 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 is an increase compared to week 43 and is above the national baseline of 2.5%. All ten HHS regions 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 Screen
Outpatient 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 increasing in all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years).

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 44 (Week ending Nov. 5, 2022)	Week 43 (Week ending Oct. 29, 2022)	Week 44 (Week ending Nov. 5, 2022)	Week 43 (Week ending Oct. 29, 2022)
Very High	16	1	71	9
High	9	4	132	24
Moderate	6	4	91	38
Low	10	12	136	109
Minimal	14	34	256	507
Insufficient Data	0	0	243	242

*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 44, 141 (1.0%) of 14,225 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 1,472 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and November 5, 2022; 96.1% were associated with influenza A virus, 2.7% were associated with influenza B virus, 0.5% with influenza A virus and influenza B virus co-infection, and 0.7% with influenza virus for which the type was not determined. Among 192 hospitalizations with influenza A subtype information, 25.0% were A(H1N1)pdm09 virus and 74.5% were A(H3N2).

The overall cumulative hospitalization rate per 100,000 population was 5.0. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 44 during previous seasons going back to 2010-2011, which ranged from 0.1 to 0.7. The highest hospitalization rates per 100,000 population were among adults aged ≥ 65 years (10.7), followed by children aged 0-4 years (9.3), adults aged 50-64 (4.9), children aged 5-17 years (5.0), and adults aged 18-49 years (2.6).

Cumulative hospitalization rates for each age group were higher than cumulative in-season hospitalization rates previously observed during week 44; since 2010-11, in-season rates ranged from 0 to 1.1 among children 0-4 years, 0 to 0.4 among children 5-17 years, 0 to 0.3 among adults 18-49 years, 0.1 to 0.9 among adults 50-64 years, and 0.2 to 2.3 among adults ≥ 65 years.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 44, 6,465 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on November 10, 2022, 9.0% of the deaths that occurred during the week ending November 5, 2022 (week 44), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.1% for this week. Among the 2,135 PIC deaths reported for this week, 949 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 54 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 Data | 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 2022-2023 season were reported to CDC during week 44. The deaths occurred during weeks 41 (the week ending October 15, 2022), 43 (the week ending October 29, 2022), and 44 (the week ending November 5, 2022). All three deaths were associated with influenza A viruses. Two of the influenza A viruses had subtyping performed; one was an A(H1N1)pdm09 virus and one was an A(H3) virus.

A total of five influenza-associated pediatric deaths occurring during the 2022-2023 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · November 18, 2022, 05:34 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated November 18, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Note: Due to the Thanksgiving holiday, FluView for Week 46 will be posted on November 28, 2022.

Key Updates for Week 45, ending November 12, 2022

Seasonal influenza activity is elevated across the country.
Viruses

Clinical Lab14.7%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization are summarized in this report.
Illness

Outpatient Respiratory Illness5.8%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 6 jurisdictions experienced moderate activity and 30 jurisdictions experienced high or very high activity.

Long-term Care Facilities1.2%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET8.1 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations8,707

patients admitted to hospitals with influenza
this week.

NCHS Mortality9.4%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)

Pediatric Deaths2

deaths were reported this week for a total of 7 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

Seasonal influenza activity is elevated across the country.
The majority of influenza viruses detected this season have been influenza A(H3N2) viruses, but the proportion of subtyped influenza A viruses that are A(H1N1) is increasing slightly.
Two more influenza-associated pediatric deaths were reported this week, for a total of seven pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 4.4 million illnesses, 38,000 hospitalizations, and 2,100 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 45 during every previous season since 2010-2011.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually. Now is a good time to get vaccinated.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing. Percent positivity increased ≥ 0.5 percentage points this week in regions 1, 2, 3, 5, 7, 8, and 10. The majority of viruses detected so far this season have been influenza A(H3N2), however during the past three week, approximately 26% of the subtyped influenza A viruses have been influenza A(H1N1)pdm09 viruses. 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	103,830	575,479
No. of positive specimens (%)	15,308 (14.7%)	49,726 (8.6%)
*Positive specimens by type*
Influenza A	15,185 (99.2%)	49,064 (98.7%)
Influenza B	123 (0.8%)	662 (1.3%)

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	7,575	53,659
No. of positive specimens	912	4,493
*Positive specimens by type/subtype*
Influenza A	911 (99.9%)	4,459 (99.2%)
(H1N1)pdm09	121 (24.6%)	807 (22.8%)
H3N2	370 (75.4%)	2,733 (77.2%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	420	918
Influenza B	1 (0.1%)	34 (0.8%)
Yamagata lineage	0	0
Victoria lineage	0	18 (100%)
Lineage not performed	1	16

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 according to 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 genetically characterized 589 influenza viruses collected since May 1, 2022.

A/H1	74
		6B.1A	74 (100%)	5a.1	5 (6.8%)
				5a.2	69 (93.2%)
A/H3	510
		3C.2a1b	510 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	510 (100%)
		3C.3a	0	3a	0
B/Victoria	5
		V1A	5 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	5 (100%)
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 2022-2023 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: Thirty-three A(H1N1)pdm09 viruses were antigenically characterized by HI, and 31 (94%) 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 31 (94%) 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): Fifty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 48 (96%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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. Virus antiviral susceptibility data will be reported later this season when a sufficient number of specimens have been tested.
Outpatient Respiratory Illness Surveillance

The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as 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 45, 5.8% 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 is above the national baseline of 2.5%. All 10 HHS regions 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 Screen
Outpatient 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 increasing in the 0-4 years, 25-49 years, 50-64 years, and 65+ years age groups, while remaining stable in the 5-24 years age group.

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 45 (Week ending Nov. 12, 2022)	Week 44 (Week ending Nov. 5, 2022)	Week 45 (Week ending Nov. 12, 2022)	Week 44 (Week ending Nov. 5, 2022)
Very High	16	16	66	74
High	14	9	150	132
Moderate	6	7	101	94
Low	11	7	139	134
Minimal	8	16	225	262
Insufficient Data	0	0	248	233

*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 45, 174 (1.2%) of 14,161 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 2,370 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and November 12, 2022; 95.6% were associated with influenza A virus, 2.4% were associated with influenza B virus, 0.3% with influenza A virus and influenza B virus co-infection, and 1.6% with influenza virus for which the type was not determined. Among 317 hospitalizations with influenza A subtype information, 23.3% were A(H1N1)pdm09 virus and 76.7% were A(H3N2).

The overall cumulative hospitalization rate per 100,000 population was 8.1. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 45 during previous seasons going back to 2010-2011, which ranged from 0.1 to 0.9. The highest hospitalization rates per 100,000 population were among adults aged ≥ 65 years (18.6), followed by children aged 0-4 years (13.6), adults aged 50-64 (8.0), children aged 5-17 years (7.3), and adults aged 18-49 years (4.2).

Cumulative hospitalization rates for each age group were higher than cumulative in-season hospitalization rates previously observed during week 45; since 2010-11 in-season rates ranged from 0 to 1.6 among children 0-4 years, 0 to 0.5 among children 5-17 years, 0 to 0.4 among adults 18-49 years, 0.1 to 0.9 among adults 50-64 years, and 0.3 to 2.7 among adults ≥ 65 years.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 45, 8,707 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on November 17, 2022, 9.4% of the deaths that occurred during the week ending November 12, 2022 (week 45), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.2% for this week. Among the 2,175 PIC deaths reported for this week, 926 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 70 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza remains small but is increasing. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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 2022-2023 season were reported to CDC during week 45. One death was associated with an influenza A(H1N1)pdm09 virus and one death was associated with an influenza A(H3) virus. Both deaths occurred during week 44 (the week ending November 5, 2022).

A total of seven influenza-associated pediatric deaths occurring during the 2022-2023 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · December 2, 2022, 06:32 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated December 2, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 47, ending November 26, 2022

Seasonal influenza activity is high and continues to increase across the country.
Viruses

Clinical Lab25.1%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization are summarized in this report.
Illness

Outpatient Respiratory Illness7.5%

of visits to a health care provider are for respiratory illness this week
(above baseline)

Outpatient Respiratory Illness: Activity Map
This week, 2 jurisdictions experienced moderate activity and 47 jurisdictions experienced high or very high activity.

Long-term Care Facilities2.6%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET16.6 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations19,593

patients admitted to hospitals with influenza
this week.

NCHS Mortality9.7%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold)

Pediatric Deaths2

deaths were 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

Seasonal influenza activity is high and continues to increase across the country.
Of influenza A viruses detected and subtyped this season, 79% have been influenza A(H3N2) and 21% have been influenza A(H1N1).
Two influenza-associated pediatric deaths were reported this week, for a total of 14 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 8.7 million illnesses, 78,000 hospitalizations, and 4,500 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 47 during every previous season since 2010-2011.
The number of flu hospital admissions reported in the HHS Protect system during week 47 almost doubled compared with week 46.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to influenza antivirals.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually. Now is a good time to get vaccinated if you haven’t already.
There are also prescription flu antiviral drugs that can be used to treat flu illness; those need to be started as early as possible.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing. Percent positivity increased ≥ 0.5 percentage points this week in all regions. 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	130,584	907,795
No. of positive specimens (%)	32,733 (25.1%)	113,482 (12.5%)
*Positive specimens by type*
Influenza A	32,594 (99.6%)	112,488 (99.1%)
Influenza B	139 (0.4%)	994 (0.9%)

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	7,447	73,201
No. of positive specimens	1,264	8,437
*Positive specimens by type/subtype*
Influenza A	1,263 (99.9%)	8,391 (99.5%)
(H1N1)pdm09	123 (15.6%)	1,469 (21.2%)
H3N2	667 (84.4%)	5,463 (78.8%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	473	1,458
Influenza B	1 (0.1%)	46 (0.5%)
Yamagata lineage	0	0
Victoria lineage	0	25 (100%)
Lineage not performed	1	21

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 according to 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 genetically characterized 788 influenza viruses collected since May 1, 2022.

A/H1	135
		6B.1A	135 (100%)	5a.1	5 (3.7%)
				5a.2	130 (96.3%)
A/H3	643
		3C.2a1b	643 (100%)	1a	0
				1b	0
				2a	0
				2a.1	1 (0.2%)
				2a.2	642 (99.8%)
		3C.3a	0	3a	0
B/Victoria	10
		V1A	10 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	10 (100%)
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 2022-2023 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: Forty-eight A(H1N1)pdm09 viruses were antigenically characterized by HI, and 46 (96%) 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 46 (96%) 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): Sixty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 58 (97%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	337	106	223	8	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	337	106	223	8	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	337	106	223	8	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	331	101	221	9	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 respiratory illness referred to as 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 47, 7.5% 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 is above the national baseline of 2.5%. All 10 HHS regions are above their respective baselines. The percent of patient visits for respiratory illness remained stable (change of ≤ .1 percentage points) in Region 6, and increased in all other regions during week 47 compared to week 46. 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 Screen
Outpatient 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 increased in all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years).

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 47 (Week ending Nov. 26, 2022)	Week 46 (Week ending Nov. 19, 2022)	Week 47 (Week ending Nov. 26, 2022)	Week 46 (Week ending Nov. 19, 2022)
Very High	31	19	107	66
High	16	17	201	173
Moderate	2	9	122	112
Low	4	5	130	135
Minimal	2	5	117	206
Insufficient Data	0	0	252	237

*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 47, 364 (2.6%) of 13,991 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 4,863 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and November 26, 2022. The overall cumulative hospitalization rate was 16.6 per 100,000 population. This cumulative hospitalization rate is higher than the cumulative in-season hospitalization rate observed in week 47 during previous seasons going back to 2010-2011, which ranged from 0.1 to 2.0.

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (39.9). Among adults aged 65 and older, rates were highest among adults aged 85 and older (71.3). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (28.4) followed by adults aged 50-64 years (16.6). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (30.2), followed by non-Hispanic American Indian or Alaska Native persons (16.7), followed by Hispanic/Latino persons (9.9), followed by non-Hispanic White persons (9.6), followed by non-Hispanic Asian/Pacific Islander persons (6.7).

Among 4,863 hospitalizations, 4,676 (96.2%) were associated with influenza A virus, 96 (2%) with influenza B virus, 9 (0.2%) with influenza A virus and influenza B virus co-infection, and 82 (1.7%) with influenza virus for which the type was not determined. Among 715 hospitalizations with influenza A subtype information, 556 (77.8%) were A(H3N2), and 159 (22.2%) were A(H1N1)pdm09. Based on preliminary data, of the 555 laboratory-confirmed influenza-associated hospitalizations with more complete data, 4.32% (95% CI: 2.79%-6.37%) also tested positive for SARS-CoV-2.

Among 522 hospitalized adults with information on underlying medical conditions, 96.7% had at least one reported underlying medical condition; the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, chronic lung disease, and obesity. Among 99 hospitalized children with information on underlying medical conditions, 73.7% 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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 47, 19,593 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on December 1, 2022, 9.7% of the deaths that occurred during the week ending November 26, 2022 (week 47), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.4% for this week. Among the 1,801 PIC deaths reported for this week, 792 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 99 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza is increasing. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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 2022-2023 season were reported to CDC during week 47. One death was associated with an influenza A(H1N1)pdm09 virus and occurred during week 46 (the week ending November 19, 2022). The other death was associated with an influenza A virus for which no subtyping was performed and occurred during week 44 (the week ending November 5, 2022).

A total of 14 influenza-associated pediatric deaths occurring during the 2022-2023 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · December 9, 2022, 05:35 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated December 9, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 48, ending December 3, 2022

Seasonal influenza activity remains high across the country.
Viruses

Clinical Lab24.8%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness7.2%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 4 jurisdictions experienced moderate activity and 46 jurisdictions experienced high or very high activity.

Long-term Care Facilities5.4%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET26.0 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations25,906

patients admitted to hospitals with influenza
this week.

NCHS Mortality10.3%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

Pediatric Deaths7

deaths were reported this week for a total of 21 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

Seasonal influenza activity is high across the country.
Of influenza A viruses detected and subtyped during week 48, 76% have been influenza A(H3N2) and 24% have been influenza A(H1N1).
Seven influenza-associated pediatric deaths were reported this week, for a total of 21 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 13 million illnesses, 120,000 hospitalizations, and 7,300 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 48 during every previous season since 2010-2011.
The number of flu hospital admissions reported in the HHS Protect system increased during week 48 compared to week 47.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to influenza antivirals.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually. Now is a good time to get vaccinated if you haven’t already.
There are also prescription flu antiviral drugs that can be used to treat flu illness. It’s very important that flu antiviral drugs are started as soon as possible to treat patients who are hospitalized with flu, people who are very sick with flu but who do not need to be hospitalized, and people with flu who are at higher risk of serious flu complications based on their age or health.
Multiple respiratory viruses are currently co-circulating with influenza. Testing is important to determine appropriate treatment.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is increasing. Percent positivity increased ≥ 0.5 percentage points this week in regions 1, 2, 8, and 9, and remained stable or decreased in all remaining regions. 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	143,924	1,058,393
No. of positive specimens (%)	35,704 (24.8%)	150,865 (14.3%)
*Positive specimens by type*
Influenza A	35,568 (99.6%)	149,704 (99.2%)
Influenza B	136 (0.4%)	1,161 (0.8%)

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	9,844	84,961
No. of positive specimens	1,974	11,695
*Positive specimens by type/subtype*
Influenza A	1,974 (100%)	11,646 (99.6%)
(H1N1)pdm09	244 (23.9%)	1,980 (21.4%)
H3N2	776 (76.1%)	7,284 (78.6%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	954	2,381
Influenza B	0 (0%)	49 (0.4%)
Yamagata lineage	0	0
Victoria lineage	0	27 (100%)
Lineage not performed	0	22

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 according to 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 genetically characterized 887 influenza viruses collected since May 1, 2022.

A/H1	171
		6B.1A	171 (100%)	5a.1	5 (2.9%)
				5a.2	166 (97.1%)
A/H3	704
		3C.2a1b	704 (100%)	1a	0
				1b	0
				2a	0
				2a.1	1 (0.1%)
				2a.2	703 (99.9%)
		3C.3a	0	3a	0
B/Victoria	12
		V1A	12 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	12 (100%)
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 2022-2023 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: Fifty-four A(H1N1)pdm09 viruses were antigenically characterized by HI, and 52 (96%) 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 52 (96%) 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): Sixty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 58 (97%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: One influenza B/Victoria-lineage virus was antigenically characterized by HI; it was well recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	397	128	260	9	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	397	128	260	9	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	397	128	260	9	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	379	119	251	9	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 respiratory illness referred to as 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 48, 7.2% 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 is above the national baseline of 2.5%. All 10 HHS regions are above their respective baselines. The percent of patient visits for respiratory illness increased in regions 1 and 2, and decreased in all other regions during week 48 compared to week 47. 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 Screen
Outpatient 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 decreased in the 0-4 years and 5-24 years age groups and increased in the 25-49 years, 50-64 years, and 65+ years age groups.

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 48 (Week ending Dec. 3, 2022)	Week 47 (Week ending Nov. 26, 2022)	Week 48 (Week ending Dec. 3, 2022)	Week 47 (Week ending Nov. 26, 2022)
Very High	30	31	114	110
High	16	16	219	202
Moderate	4	2	115	120
Low	2	4	123	131
Minimal	3	2	118	123
Insufficient Data	0	0	240	243

*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 48, 768 (5.4%) of 14,321 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 7,598 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and December 3, 2022. The weekly hospitalization rate observed in week 48 was 5.9 per 100,000 population. The weekly rate observed during week 47 is the third highest peak weekly rate observed during all seasons going back to 2010-2011 following the 2014-15 and 2017-18 seasons.

The overall cumulative hospitalization rate was 26.0 per 100,000 population. This cumulative hospitalization rate is 9.6 times higher than the highest cumulative in-season hospitalization rate observed in week 48 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.2 per 100,000 to 2.7 per 100,000).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (67.3). Among adults aged 65 and older, rates were highest among adults aged 85 and older (119.9). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (42.3) followed by adults aged 50-64 years (26.2). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (43.9), followed by non-Hispanic American Indian or Alaska Native persons (29.0), followed by non-Hispanic White persons (16.5) and Hispanic/Latino persons (16.5), followed by non-Hispanic Asian/Pacific Islander persons (10.7).

Among 7,598 hospitalizations, 7,264 (95.6%) were associated with influenza A virus, 135 (1.8%) with influenza B virus, 10 (0.1%) with influenza A virus and influenza B virus co-infection, and 189 (2.5%) with influenza virus for which the type was not determined. Among 1268 hospitalizations with influenza A subtype information, 1016 (80.1%) were A(H3N2), and 252 (19.9%) were A(H1N1)pdm09. Based on preliminary data, of the 798 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.76% (95% CI: 2.55%-5.32%) also tested positive for SARS-CoV-2.

Among 699 hospitalized adults with information on underlying medical conditions, 96.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 163 hospitalized children with information on underlying medical conditions, 71.2% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.

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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 48, 25,906 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on December 8, 2022, 10.3% of the deaths that occurred during the week ending December 3, 2022 (week 48), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.5% for this week. Among the 2,484 PIC deaths reported for this week, 968 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 246 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza is increasing. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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

Seven influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 48. The deaths occurred between week 42 (the week ending October 22, 2022) and week 48 (the week ending December 3, 2022). All seven deaths were associated with influenza A viruses. Four of the influenza A viruses had subtyping performed; all four were A(H3) viruses.

A total of 21 influenza-associated pediatric deaths occurring during the 2022-2023 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.

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization:
Additional influenza surveillance information from participating WHO member nations is available through
FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza:
Australia, China, Japan, the United Kingdom, 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 Control.

Public Health Agency of Canada:
The most up-to-date influenza information from Canada is available in Canada’s weekly FluWatch report.

Public Health England:
The most up-to-date influenza information from the United Kingdom is available from Public Health England.

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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · December 16, 2022, 05:01 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated December 16, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 49, ending December 10, 2022

Seasonal influenza activity remains high but appears to be declining in some areas.
Viruses

Clinical Lab25.4%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness6.9%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 48 jurisdictions experienced high or very high activity.

Long-term Care Facilities6.8%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET32.7 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations23,503

patients admitted to hospitals with influenza
this week.

NCHS Mortality11.6%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

Pediatric Deaths9

deaths were reported this week for a total of 30 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

Seasonal influenza activity remains high but appears to be declining in some areas.
Of influenza A viruses detected and subtyped during week 49, 80% were influenza A(H3N2) and 20% were influenza A(H1N1).
Nine influenza-associated pediatric deaths were reported this week, for a total of 30 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 15 million illnesses, 150,000 hospitalizations, and 9,300 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate observed in week 49 during every previous season since 2010-2011.
The number of flu hospital admissions reported in the HHS Protect system decreased nationally during week 49 compared to week 48.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to the influenza antivirals oseltamivir, peramivir, zanamivir, and baloxavir.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually. Now is a good time to get vaccinated if you haven’t already.
CDC issued Interim Guidance for Clinicians to Prioritize Antiviral Treatment of Influenza in the Setting of Reduced Availability of Oseltamivir through the Health Alert Network (HAN) on December 15, 2022.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories is the same as the previous week. Percent positivity increased ≥ 0.5 percentage points this week in regions 1, 5, 7, and 8, and remained stable or decreased in all remaining regions. 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	123,987	1,219,825
No. of positive specimens (%)	31,442 (25.4%)	192,458 (15.8%)
*Positive specimens by type*
Influenza A	31,287 (99.5%)	191,112 (99.3%)
Influenza B	155 (0.5%)	1,346 (0.7%)

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	8,996	96,317
No. of positive specimens	1,763	14,494
*Positive specimens by type/subtype*
Influenza A	1,760 (99.8%)	14,440 (99.6%)
(H1N1)pdm09	190 (20.2%)	2,480 (21.5%)
H3N2	750 (79.8%)	9,054 (78.5%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	820	2,905
Influenza B	3 (0.2%)	54 (0.4%)
Yamagata lineage	0	0
Victoria lineage	1 (100%)	30 (100%)
Lineage not performed	2	24

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 according to 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 genetically characterized 1,010 influenza viruses collected since May 1, 2022.

A/H1	214
		6B.1A	214 (100%)	5a.1	5 (2.3%)
				5a.2	209 (97.7%)
A/H3	784
		3C.2a1b	784 (100%)	1a	0
				1b	0
				2a	0
				2a.1	1 (0.1%)
				2a.2	783 (99.9%)
		3C.3a	0	3a	0
B/Victoria	12
		V1A	12 (100%)	V1A	0
				V1A.1	0
				V1A.3	0
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	12 (100%)
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 2022-2023 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: Sixty-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 63 (97%) 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 63 (97%) 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): Sixty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 58 (97%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: Eight influenza B/Victoria-lineage virus were antigenically characterized by HI; all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	519	171	338	10	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	519	171	338	10	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	519	171	338	10	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	501	162	330	9	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 respiratory illness referred to as 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 49, 6.9% 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 is above the national baseline of 2.5%. All 10 HHS regions are above their respective baselines. The percent of patient visits for respiratory illness increased in regions 1, 7, and 8, decreased in regions 2, 3, 4, 6, 9, and 10, and remained stable in region 5 during week 49 compared to week 48. 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 Screen
Outpatient 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 increased in 5-24 years age group and decreased in all other age groups (0-4 years, 25-49 years, 50-64 years, and 65+ years).

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 49 (Week ending Dec. 10, 2022)	Week 48 (Week ending Dec. 3, 2022)	Week 49 (Week ending Dec. 10, 2022)	Week 48 (Week ending Dec. 3, 2022)
Very High	28	32	85	115
High	20	14	228	224
Moderate	3	3	150	113
Low	2	3	114	126
Minimal	2	3	118	119
Insufficient Data	0	0	234	232

*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 49, 971 (6.8%) of 14,315 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 9,567 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and December 10, 2022. The weekly hospitalization rate observed in week 49 was 4.5 per 100,000 population. The weekly rate observed during week 48 (8.0 per 100,000 population), the highest so far this season, is the third highest peak weekly rate observed during all seasons going back to 2010-2011 following the 2014-15 and 2017-18 seasons.

The overall cumulative hospitalization rate was 32.7 per 100,000 population. This cumulative hospitalization rate is 7.6 times higher than the highest cumulative in-season hospitalization rate observed in week 49 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.2 per 100,000 to 4.3 per 100,000).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (88.4). Among adults aged 65 and older, rates were highest among adults aged 85 and older (160.2). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (49.6) followed by adults aged 50-64 years (33.6). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (47.9), followed by non-Hispanic American Indian or Alaska Native persons (35.9), followed by Hispanic/Latino persons (22.5), followed by non-Hispanic White persons (20.7) and followed by non-Hispanic Asian/Pacific Islander persons (13.5).

Among 9,567 hospitalizations, 9,287 (97.1%) were associated with influenza A virus, 150 (1.6%) with influenza B virus, 13 (0.1%) with influenza A virus and influenza B virus co-infection, and 117 (1.2%) with influenza virus for which the type was not determined. Among 1761 hospitalizations with influenza A subtype information, 1,394 (79.2%) were A(H3N2) and 367 (20.8%) were A(H1N1)pdm09. Based on preliminary data, of the 1,047 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.2% (95% CI: 2.18%-4.40%) also tested positive for SARS-CoV-2.

Among 846 hospitalized adults with information on underlying medical conditions, 96.8% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 237 hospitalized children with information on underlying medical conditions, 70.5% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.

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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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 49, 23,503 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on December 15, 2022, 11.6% of the deaths that occurred during the week ending December 10, 2022 (week 49), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.6% for this week. Among the 2,913 PIC deaths reported for this week, 1,179 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 331 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza is increasing. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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

Nine influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 49. The deaths occurred between week 44 (the week ending November 5, 2022) and week 49 (the week ending December 10, 2022). Eight deaths were associated with influenza A viruses and one death was associated with an influenza B virus with no lineage determined. Five of the influenza A viruses had subtyping performed; all five were A(H3) viruses.

A total of 30 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

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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.

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · December 23, 2022, 01:01 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated December 23, 2022

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 50, ending December 17, 2022

Seasonal influenza activity remains high but is declining in most areas.
Viruses

Clinical Lab24.4%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness6.3%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 3 jurisdictions experienced moderate activity and 48 jurisdictions experienced high or very high activity.

Long-term Care Facilities6.1%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET39.9 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations20,783

patients admitted to hospitals with influenza
this week.

NCHS Mortality12.0%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

Pediatric Deaths17

deaths were reported this week for a total of 47 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

Seasonal influenza activity remains high but is declining in most areas.
Of influenza A viruses detected and subtyped during week 50, 77.8% were influenza A(H3N2) and 22.2% were influenza A(H1N1).
Seventeen influenza-associated pediatric deaths were reported this week, for a total of 47 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 18 million illnesses, 190,000 hospitalizations, and 12,000 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system was more than 6 times higher than the highest cumulative in-season hospitalization rate observed for week 50 during previous seasons going back to 2010-2011. However, this in-season rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons going back to 2010-11.
The number of flu hospital admissions reported in the HHS Protect system decreased nationally from the week prior for the second week in a row.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to the influenza antivirals oseltamivir, peramivir, zanamivir, and baloxavir.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC recommends that everyone ages 6 months and older get a flu vaccine annually. Now is a good time to get vaccinated if you haven’t already.
CDC issued Interim Guidance for Clinicians to Prioritize Antiviral Treatment of Influenza in the Setting of Reduced Availability of Oseltamivir through the Health Alert Network (HAN) on December 15, 2022.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories declined compared to the previous week. Percent positivity increased ≥ 0.5 percentage points this week in Region 7 and remained stable or decreased in all remaining regions. 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	135,848	1,400,183
No. of positive specimens (%)	33,202 (24.4%)	237,237 (16.9 %)
*Positive specimens by type*
Influenza A	33,041 (99.5%)	235,705 (99.4%)
Influenza B	161 (0.5%)	1,532 (0.6%)

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	9,081	107,874
No. of positive specimens	1,588	17,454
*Positive specimens by type/subtype*
Influenza A	1,583 (99.7%)	17,393 (99.7%)
(H1N1)pdm09	182 (22.2%)	3,005 (21.5%)
H3N2	637 (77.8%)	10,943 (78.5%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	764	3,444
Influenza B	5 (0.3%)	61 (0.3%)
Yamagata lineage	0	0
Victoria lineage	2 (100%)	36 (100%)
Lineage not performed	3	25

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 according to 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 genetically characterized 1,286 influenza viruses collected since May 1, 2022.

A/H1	299
		6B.1A	299 (100%)	5a.1	6 (2.0%)
				5a.2	293 (98.0%)
A/H3	968
		3C.2a1b	968 (100%)	1a	0
				1b	0
				2a	0
				2a.1	1 (0.1%)
				2a.2	967 (99.9%)
		3C.3a	0	3a	0
B/Victoria	19
		V1A	19 (100%)	V1A	0
				V1A.1	0
				V1A.3	1 (5.3%)
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	18 (94.7%)
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 2022-2023 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: Seventy-five A(H1N1)pdm09 viruses were antigenically characterized by HI, and 73 (97%) 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 73 (97%) 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): Sixty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 58 (97%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: Eight influenza B/Victoria-lineage virus were antigenically characterized by HI; all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	739	232	492	15	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	739	232	492	15	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	739	232	492	15	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	713	222	476	15	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 respiratory illness referred to as 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 50, 6.3% 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 is above the national baseline of 2.5%. All 10 HHS regions are above their respective baselines. The percent of patient visits for respiratory illness increased in Region 8, remained stable in regions 1 and 7, and decreased in the remaining seven regions during week 50 compared to week 49. 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 Screen
Outpatient 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 decreased in all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years).

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 50 (Week ending Dec. 17, 2022)	Week 49 (Week ending Dec. 10, 2022)	Week 50 (Week ending Dec. 17, 2022)	Week 49 (Week ending Dec. 10, 2022)
Very High	27	28	71	85
High	21	20	190	231
Moderate	3	3	162	151
Low	2	2	121	112
Minimal	1	2	131	120
Insufficient Data	1	0	254	230

*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 50, 869 (6.1%) of 14,266 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 11,671 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2021, and December 17, 2022. The weekly hospitalization rate observed in week 50 was 4.4 per 100,000 population. The weekly rate observed during week 48 (week ending December 3) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season which peaked during week 1 (week ending January 6) and the 2014-15 season which peaked during week 52 (week ending December 27).

The overall cumulative hospitalization rate was 39.9 per 100,000 population. This cumulative hospitalization rate is 6.4 times higher than the highest cumulative in-season hospitalization rate observed in week 50 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.3 per 100,000 to 6.2 per 100,000). However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, 2010-11 seasons).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (110.1). Among adults aged 65 and older, rates were highest among adults aged 85 and older (196.8). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (58.8) followed by adults aged 50-64 years (41.7). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (57.2), followed by non-Hispanic American Indian or Alaska Native persons (46.2), followed by Hispanic/Latino persons (28.8), followed by non-Hispanic White persons (27.3) and followed by non-Hispanic Asian/Pacific Islander persons (16.4).

Among 11,671 hospitalizations,11,335 (97.1%) were associated with influenza A virus, 178 (1.5%) with influenza B virus, 14 (0.1%) with influenza A virus and influenza B virus co-infection, and 144 (1.2%) with influenza virus for which the type was not determined. Among 2,131 hospitalizations with influenza A subtype information, 1,693 (79.4%) were A(H3N2), and 438 (20.6%) were A(H1N1)pdm09. Based on preliminary data, of the 1,316 laboratory-confirmed influenza-associated hospitalizations with more complete data, 2.96% (95% CI: 2.12%-4.03%) also tested positive for SARS-CoV-2.

Among 995 hospitalized adults with information on underlying medical conditions, 96.9% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 318 hospitalized children with information on underlying medical conditions, 70.4% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.

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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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 50, 20,783 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on December 22, 2022, 12.0% of the deaths that occurred during the week ending December 17, 2022 (week 50), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage is above the epidemic threshold of 6.7% for this week. Among the 3,026 PIC deaths reported for this week, 1,232 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 408 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza is increasing. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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

Seventeen influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 50. The deaths occurred between week 44 (the week ending November 5, 2022) and week 50 (the week ending December 17, 2022). All 17 deaths were associated with influenza A viruses. Subtyping was performed on eight of the influenza A viruses; all eight were A(H3) viruses.

A total of 47 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

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Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · January 6, 2023, 02:39 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated January 6, 2023

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 52, ending December 31, 2022

Seasonal influenza activity remains high but continues to decline in most areas.
Viruses

Clinical Lab15.0%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness5.4%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 8 jurisdictions experienced moderate activity and 39 jurisdictions experienced high or very high activity.

Long-term Care Facilities5.5%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET48.6 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations18,954

patients admitted to hospitals with influenza
this week.

NCHS Mortality12.8%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

Pediatric Deaths13

deaths were reported this week for a total of 74 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

Seasonal influenza activity remains high but continues to decline in most areas.
Of influenza A viruses detected and subtyped during week 52, 70% were influenza A(H3N2) and 30% were influenza A(H1N1).
Thirteen influenza-associated pediatric deaths were reported this week, for a total of 74 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 22 million illnesses, 230,000 hospitalizations, and 14,000 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system was 3.5 times higher than the highest cumulative in-season hospitalization rate observed for week 52 during previous seasons going back to 2010-2011. However, this in-season rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons going back to 2010-2011.
The number of flu hospital admissions reported in the HHS Protect system was similar to last week.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to the influenza antivirals oseltamivir, peramivir, zanamivir, and baloxavir.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
CDC issued Interim Guidance for Clinicians to Prioritize Antiviral Treatment of Influenza in the Setting of Reduced Availability of Oseltamivir through the Health Alert Network (HAN) on December 15, 2022.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories declined compared to the previous week. Percent positivity decreased in all HHS regions. 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	93,589	1,660,415
No. of positive specimens (%)	14,027 (15.0%)	287,354 (17.3%)
*Positive specimens by type*
Influenza A	13,905 (99.1%)	285,535 (99.4%)
Influenza B	122 (0.9%)	1,819 (0.6%)

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	5,389	123,258
No. of positive specimens	613	21,054
*Positive specimens by type/subtype*
Influenza A	611 (99.7%)	20,982 (99.7%)
(H1N1)pdm09	79 (29.8%)	3,701 (22.0%)
H3N2	186 (70.2%)	13,111 (22.0%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	346	4,169
Influenza B	2 (0.3%)	72 (0.3%)
Yamagata lineage	0	0
Victoria lineage	1 (100%)	43 (100%)
Lineage not performed	1	29

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 according to 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 genetically characterized 1,481 influenza viruses collected since May 1, 2022.

A/H1	368
		6B.1A	368 (100%)	5a.1	6 (1.6%)
				5a.2	362 (98.4%)
A/H3	1,094
		3C.2a1b	1,040 (100%)	1a	0
				1b	0
				2a	0
				2a.1	1 (0.1%)
				2a.2	1,093 (99.9%)
		3C.3a	0	3a	0
B/Victoria	19
		V1A	19 (100%)	V1A	0
				V1A.1	0
				V1A.3	1 (5.3%)
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	18 (94.7%)
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 2022-2023 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: Eighty-nine A(H1N1)pdm09 viruses were antigenically characterized by HI, and 87 (98%) 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 87 (98%) 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): Sixty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 58 (97%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: Eleven influenza B/Victoria-lineage virus were antigenically characterized by HI; all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	895	293	586	16	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	895	293	586	16	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	895	293	586	16	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	871	280	575	16	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 respiratory illness referred to as 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 52, 5.4% 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 is above the national baseline of 2.5%. All 10 HHS regions are above their respective baselines. The percent of patient visits for respiratory illness remained stable for regions 4 and 9 and decreased in all other regions during week 52 compared to week 51. 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 Screen
Outpatient 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 increased in the 65+ years age group, remained stable in the 50-64 years age group, and decreased in the 0-4 years, 5-24 years, and 25-49 years age groups.

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 52 (Week ending Dec. 31, 2022)	Week 51 (Week ending Dec. 24, 2022)	Week 52 (Week ending Dec. 31, 2022)	Week 51 (Week ending Dec. 24, 2022)
Very High	12	24	37	59
High	27	20	155	172
Moderate	8	4	142	152
Low	3	1	167	154
Minimal	5	6	167	147
Insufficient Data	0	0	261	245

*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 52, 786 (5.5%) of 14,188 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 14,217 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and December 31, 2022. The weekly hospitalization rate observed in week 52 was 2.6 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season which peaked during week 1 (week ending January 6, 2018) and the 2014-15 season which peaked during week 52 (week ending December 27, 2014).

The overall cumulative hospitalization rate was 48.6 per 100,000 population. This cumulative hospitalization rate is 3.5 times higher than the highest cumulative in-season hospitalization rate observed in week 52 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.3 per 100,000 to 13.8 per 100,000). However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, and 2010-11 seasons).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (137.9). Among adults aged 65 and older, rates were highest among adults aged 85 and older (246.7). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (70.2), followed by adults aged 50-64 years (51.1). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (71.1), followed by non-Hispanic American Indian or Alaska Native persons (59.5), non-Hispanic White persons (38.4), Hispanic/Latino persons (36.2), and non-Hispanic Asian/Pacific Islander persons (20.9).

Among 14,217 hospitalizations, 13,791 (97%) were associated with influenza A virus, 222 (1.6%) with influenza B virus, 18 (0.1%) with influenza A virus and influenza B virus co-infection, and 186 (1.3%) with influenza virus for which the type was not determined. Among 2,547 hospitalizations with influenza A subtype information, 2,007 (78.8%) were A(H3N2), and 540 (21.2%) were A(H1N1)pdm09. Based on preliminary data, of the 1,608 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.2% (95% CI: 2.4%-4.2%) also tested positive for SARS-CoV-2.

Among 1,220 hospitalized adults with information on underlying medical conditions, 96.4% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 551 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 227 (41.2%) were pregnant. Among 383 hospitalized children with information on underlying medical conditions, 67.1% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity, and neurologic disease.

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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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 52, 18,954 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on January 5, 2023, 12.8% of the deaths that occurred during the week ending December 31, 2022 (week 52), 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 2,380 PIC deaths reported for this week, 1,023 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 303 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through early December and has remained at similar levels for the past four weeks. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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

Thirteen influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 52. The deaths occurred between week 43 (the week ending October 29, 2022) and week 51 (the week ending December 24, 2022). Twelve deaths were associated with influenza A viruses and one was associated with an influenza B virus with no lineage determined. Six of the influenza A viruses had subtyping performed; one was an A(H1N1) virus and the remaining five were A(H3) viruses.

A total of 74 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

View Full Screen

Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · January 13, 2023, 05:02 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated January 13, 2023

Note: CDC is tracking the COVID-19 pandemic in a weekly publication called COVID Data Tracker Weekly Review.

Key Updates for Week 1, ending January 7, 2023

Seasonal influenza activity continues but is declining in most areas.
Viruses

Clinical Lab8.6%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness4.0%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 14 jurisdictions experienced moderate activity and 23 jurisdictions experienced high or very high activity.

Long-term Care Facilities5.1%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET54.4 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations12,409

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 Deaths5

deaths were reported this week for a total of 79 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

Seasonal influenza activity continues but is declining in most areas.
Of influenza A viruses detected and subtyped during week 1, 72% were influenza A(H3N2) and 28% were influenza A(H1N1).
Five influenza-associated pediatric deaths were reported this week, for a total of 79 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 24 million illnesses, 260,000 hospitalizations, and 16,000 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system was 1.8 times higher than the highest cumulative in-season hospitalization rate observed for week 1 during previous seasons going back to 2010-2011. However, this in-season rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons going back to 2010-2011.
The number of flu hospital admissions reported in the HHS Protect system decreased compared to week 52.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to the influenza antivirals oseltamivir, peramivir, zanamivir, and baloxavir.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
CDC issued Interim Guidance for Clinicians to Prioritize Antiviral Treatment of Influenza in the Setting of Reduced Availability of Oseltamivir through the Health Alert Network (HAN) on December 15, 2022.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories declined compared to the previous week. Percent positivity decreased in all HHS regions. 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	96,123	1,791,474
No. of positive specimens (%)	8,281 (8.6%)	300,365 (16.8%)
*Positive specimens by type*
Influenza A	8,169 (98.6%)	298,392 (99.3%)
Influenza B	112 (1.4%)	1,973 (0.7%)

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	6,724	132,276
No. of positive specimens	743	22,902
*Positive specimens by type/subtype*
Influenza A	736 (99.1%)	22,818 (99.6%)
(H1N1)pdm09	130 (28.4%)	4,245 (22.9%)
H3N2	328 (71.6%)	14,278 (77.1%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	278	4,294
Influenza B	7 (0.9%)	84 (0.4%)
Yamagata lineage	0	0
Victoria lineage	6 (100%)	53 (100%)
Lineage not performed	1	31

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 according to 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 genetically characterized 1,634 influenza viruses collected since May 1, 2022.

A/H1	431
		6B.1A	431 (100%)	5a.1	6 (1.4%)
				5a.2	425 (98.6%)
A/H3	1,184
		3C.2a1b	1,184 (100%)	1a	0
				1b	0
				2a	0
				2a.1	1 (0.1%)
				2a.2	1,183 (99.9%)
		3C.3a	0	3a	0
B/Victoria	19
		V1A	19 (100%)	V1A	0
				V1A.1	0
				V1A.3	1 (5.3%)
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	18 (94.7%)
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 2022-2023 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: Eighty-nine A(H1N1)pdm09 viruses were antigenically characterized by HI, and 87 (98%) 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 87 (98%) 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):Sixty A(H3N2) viruses were antigenically characterized by HINT; all were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines and 58 (97%) were well-recognized by ferret antisera to egg-grown A/Darwin/9/2021-like reference viruses representing the A(H3N2) component for egg-based influenza vaccines.

Influenza B Viruses

B/Victoria: Eleven influenza B/Victoria-lineage virus were antigenically characterized by HI; all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines and by ferret antisera to egg-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the egg-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	1,193	410	765	18	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	1,193	410	765	18	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	1,193	410	765	18	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	1,147	387	743	17	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 respiratory illness referred to as 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 1, 4.0% 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 is above the national baseline of 2.5%. The percent of patient visits for respiratory illness decreased for all regions during week 1 compared to week 52 but remains above their region-specific baselines in all regions. 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 Screen
Outpatient 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 decreased in all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years) in week 1 compared to week 52.

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 1 (Week ending Jan. 7, 2023)	Week 52 (Week ending Dec. 31, 2022)	Week 1 (Week ending Jan. 7, 2023)	Week 52 (Week ending Dec. 31, 2022)
Very High	2	12	19	38
High	21	31	93	158
Moderate	14	5	102	145
Low	9	2	184	169
Minimal	8	5	275	169
Insufficient Data	1	0	256	250

*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 1, 724 (5.1%) of 14,269 reporting LTCFs reported at least one influenza positive test among their residents.

View Chart Data | View Full Screen

Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 15,910 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and January 7, 2023. The weekly hospitalization rate observed in week 1 was 2.0 per 100,000 population. The weekly rate observed during week 48 (week ending December 3) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season which peaked during week 1 (week ending January 6) and the 2014-15 season which peaked during week 52 (week ending December 27).

The overall cumulative hospitalization rate was 54.4 per 100,000 population. This cumulative hospitalization rate is 1.8 times higher than the highest cumulative in-season hospitalization rate observed in week 1 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.4 per 100,000 to 30.0 per 100,000). However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, 2010-11 seasons).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (159.2). Among adults aged 65 and older, rates were highest among adults aged 85 and older (291.2). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (74.0) followed by adults aged 50-64 years (57.3). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (77.5), followed by non-Hispanic American Indian or Alaska Native persons (65.4), non-Hispanic White persons (44.7), Hispanic/Latino persons (41.1), and non-Hispanic Asian/Pacific Islander persons (23.5).

Among 15,910 hospitalizations, 15,426 (97.0%) were associated with influenza A virus, 260 (1.6%) with influenza B virus, 20 (0.1%) with influenza A virus and influenza B virus co-infection, and 204 (1.3%) with influenza virus for which the type was not determined. Among 2,881 hospitalizations with influenza A subtype information, 2,248 (78.0%) were A(H3N2), and 633 (22.0%) were A(H1N1)pdm09. Based on preliminary data, of the 1,997 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.1% (95% CI: 2.3%-3.9%) also tested positive for SARS-CoV-2.

Among 1,452 hospitalized adults with information on underlying medical conditions, 96.3% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 622 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 252 (40.5%) were pregnant. Among 511 hospitalized children with information on underlying medical conditions, 66.7% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity and neurologic disease.

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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
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 1, 12,409 patients with laboratory-confirmed influenza were admitted to a hospital.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on January 12, 2023, 13.1% of the deaths that occurred during the week ending January 7, 2023 (week 1), 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 3,151 PIC deaths reported for this week, 1,433 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 353 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through early December and has remained at similar levels for the past four weeks. The data presented are preliminary and may change as more data are received and processed.

View Chart Data | 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

Five influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 1. The deaths occurred during weeks 45, 49, 51, and 52 of 2022 (the weeks ending November 12, December 10, December 24, and December 31, respectively). All five deaths were associated with influenza A viruses. Subtyping was performed on two of the influenza A viruses; both were A(H3) viruses.

A total of 79 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

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Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · January 20, 2023, 04:32 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated January 20, 2023

Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

Key Updates for Week 2, ending January 14, 2023

Seasonal influenza activity continues to decline across the country.
Viruses

Clinical Lab4.6%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness3.0%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 8 jurisdictions experienced moderate activity and 7 jurisdictions experienced high or very high activity.

Long-term Care Facilities2.8%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET56.7 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations6,367

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 Deaths7

deaths were reported (1 occurred in 2021-22 season and 6 occurred in 2022-23 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

Seasonal influenza activity continues to decline across the country.
Three regions were below their outpatient respiratory illness baselines for the first time since October 2022.
The number of flu hospital admissions reported in the HHS Protect system decreased compared to week 1.
Of influenza A viruses detected and subtyped during week 2, 81% were influenza A(H3N2) and 19% were influenza A(H1N1).
Six influenza-associated pediatric deaths that occurred during the 2022-23 season were reported this week, for a total of 85 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 25 million illnesses, 270,000 hospitalizations, and 17,000 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system was 1.6 times higher than the highest cumulative in-season hospitalization rate observed for week 2 during previous seasons going back to 2010-2011. However, this in-season rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons going back to 2010-2011.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to the influenza antivirals oseltamivir, peramivir, zanamivir, and baloxavir.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
CDC issued Interim Guidance for Clinicians to Prioritize Antiviral Treatment of Influenza in the Setting of Reduced Availability of Oseltamivir through the Health Alert Network (HAN) on December 15, 2022.

U.S. Virologic Surveillance

Nationally, the percentage of specimens testing positive for influenza in clinical laboratories declined compared to the previous week. Percent positivity decreased in all HHS regions. 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	75,638	1,882,770
No. of positive specimens (%)	3,498 (4.6%)	305,535 (16.2%)
*Positive specimens by type*
Influenza A	3,403 (97.3%)	303,449 (99.3%)
Influenza B	95 (2.7%)	2,086 (0.7%)

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	6,315	141,009
No. of positive specimens	453	23,823
*Positive specimens by type/subtype*
Influenza A	442 (97.6%)	23,720 (99.6%)
(H1N1)pdm09	63 (18.7%)	4,498 (23.1%)
H3N2	274 (81.3%)	14,964 (76.9%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	105	4,257
Influenza B	11 (2.4%)	102 (0.4%)
Yamagata lineage	0	0
Victoria lineage	6 (100%)	65 (100%)
Lineage not performed	5	37

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 according to 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 genetically characterized 1,366 influenza viruses collected since October 2, 2022.

A/H1	470
		6B.1A	470 (100%)	5a.1	1 (0.2%)
				5a.2	469 (99.8%)
A/H3	875
		3C.2a1b	875 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	875 (100%)
		3C.3a	0	3a	0
B/Victoria	21
		V1A	19 (100%)	V1A	0
				V1A.1	0
				V1A.3	2 (9.5%)
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	19 (90.5%)
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 2022-2023 Northern Hemisphere recommended 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: Seventy-four A(H1N1)pdm09 viruses were antigenically characterized by HI, and 73 (99.9%) 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.
A (H3N2): One hundred and three A(H3N2) viruses were antigenically characterized by HINT, and 94 (91%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

Influenza B Viruses

B/Victoria: Ten influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	1,370	472	877	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	1,370	472	877	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	1,370	472	877	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	1,320	446	853	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 respiratory illness referred to as 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 2, 3.0% 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 is a decline compared to what was reported in week 1 but remains above the national baseline of 2.5%. Seven of the 10 HHS regions are above their respective baselines; regions 5, 6, and 8 are below their respective baselines. The percent of patient visits for respiratory illness decreased for all regions during week 2 compared to week 1. 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 Screen
Outpatient 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 decreased in all age groups (0-4 years, 5-24 years, 25-49 years, 50-64 years, and 65+ years) in week 2 compared to week 1.

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 2 (Week ending Jan. 14, 2023)	Week 1 (Week ending Jan. 7, 2022)	Week 2 (Week ending Jan. 14, 2023)	Week 1 (Week ending Jan. 7, 2022)
Very High	0	2	3	20
High	7	20	38	93
Moderate	8	15	67	102
Low	18	8	159	184
Minimal	22	10	396	286
Insufficient Data	0	0	266	244

*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 2, 401 (2.8%) of 14,373 reporting LTCFs reported at least one influenza positive test among their residents.

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Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 16,602 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and January 14, 2023. The weekly hospitalization rate observed in week 2 was 0.8 per 100,000 population. The weekly rate observed during week 48 (week ending December 3, 2022) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season, which peaked during week 1 (week ending January 6) and the 2014-15 season, which peaked during week 52 (week ending December 27, 2022).

The overall cumulative hospitalization rate was 56.7 per 100,000 population. This cumulative hospitalization rate is 1.6 times higher than the highest cumulative in-season hospitalization rate observed in week 2 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.5 per 100,000 to 36.3 per 100,000). However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, and 2010-11 seasons).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (166.9). Among adults aged 65 and older, rates were highest among adults aged 85 and older (306.6). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (77.3), followed by adults aged 50-64 years (59.8). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (79.3), followed by non-Hispanic American Indian or Alaska Native persons (67.4), non-Hispanic White persons (46.9), Hispanic/Latino persons (43), and non-Hispanic Asian/Pacific Islander persons (24.2).

Among 16,602 hospitalizations,16,095 (96.9%) were associated with influenza A virus, 282 (1.7%) with influenza B virus, 22 (0.1%) with influenza A virus and influenza B virus co-infection, and 203 (1.2%) with influenza virus for which the type was not determined. Among 3,042 hospitalizations with influenza A subtype information, 2,364 (77.7%) were A(H3N2) and 678 (22.3%) were A(H1N1)pdm09. Based on preliminary data, of the 2,409 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.2% (95% CI: 2.5%-4.0%) also tested positive for SARS-CoV-2.

Among 1,694 hospitalized adults with information on underlying medical conditions, 96.5% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 669 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 268 (40.1%) were pregnant. Among 608 hospitalized children with information on underlying medical conditions, 66.1% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by obesity and neurologic disease.

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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 | RESP-NET Interactive
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 2, 6,367 patients with laboratory-confirmed influenza were admitted to a hospital.

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Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on January 19, 2023, 13.1% of the deaths that occurred during the week ending January 14, 2023 (week 2), 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 2,954 PIC deaths reported for this week, 1,422 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 251 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December and has been decreasing for the past four weeks. 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

Seven influenza-associated pediatric deaths were reported to CDC during week 2.

Six of the deaths occurred during the 2022-2023 season between week 48 of 2022 (the week ending December 3, 2022) and week 1 of 2023 (the week ending January 7, 2023). All six deaths were associated with influenza A viruses. Four of the influenza A viruses had subtyping performed; three were A(H3) viruses and one was an A(H1N1) virus. A total of 85 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC

One death occurred during week 27 of the 2021-2022 season (the week ending July 9, 2022). The death was associated with an influenza A virus for which no subtyping was performed. The total number of deaths that occurred in the 2021-2022 season is 45.

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Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

**Lance** · January 27, 2023, 03:44 PM

Weekly U.S. Influenza Surveillance Report

Print
Updated January 27, 2023

Note: CDC is also tracking the impact of other respiratory viruses, including COVID-19. Data comparing the impact of these viruses can be found in two new dashboards: RESP-NET and NSSP’s Emergency Department Visits for COVID-19, Influenza and Respiratory Syncytial Virus.

Key Updates for Week 3, ending January 21, 2023

Seasonal influenza activity continues to decline across the country.
Viruses

Clinical Lab3.0%

positive for influenza
this week

Public Health Lab
The most frequently reported viruses this week were influenza A(H3N2).

Virus Characterization
Genetic and antigenic characterization and antiviral susceptibility are summarized in this report.
Illness

Outpatient Respiratory Illness2.6%

of visits to a health care provider this week were for respiratory illness
(above baseline).

Outpatient Respiratory Illness: Activity Map
This week, 7 jurisdictions experienced moderate activity and 3 jurisdictions experienced high activity.

Long-term Care Facilities1.7%

of facilities reported
≥ 1 influenza-positive test
among residents this week.
Severe Disease

FluSurv-NET58.1 per 100,000

cumulative hospitalization rate

HHS Protect Hospitalizations4,009

patients admitted to hospitals with influenza
this week.

NCHS Mortality12.0%

of deaths attributed to pneumonia, influenza, or COVID-19 this week (above threshold).

Pediatric Deaths6

deaths were reported this week for a total of
91 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

Seasonal influenza activity continues to decline across the country.
Six HHS regions were below their outpatient respiratory illness baselines.
The number of flu hospital admissions reported in the HHS Protect system decreased compared to week 2.
Of influenza A viruses detected and subtyped during week 3, 73% were influenza A(H3N2) and 27% were influenza A(H1N1).
Six influenza-associated pediatric deaths that occurred during the 2022-23 season were reported this week, for a total of 91 pediatric flu deaths reported so far this season.
CDC estimates that, so far this season, there have been at least 25 million illnesses, 280,000 hospitalizations, and 17,000 deaths from flu.
The cumulative hospitalization rate in the FluSurv-NET system was 1.4 times higher than the highest cumulative in-season hospitalization rate observed for week 3 during previous seasons going back to 2010-2011. However, this in-season rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons going back to 2010-2011.
The majority of influenza viruses tested are in the same genetic subclade as and antigenically similar to the influenza viruses included in this season’s influenza vaccine.
All viruses collected and evaluated this season have been susceptible to the influenza antivirals oseltamivir, peramivir, zanamivir, and baloxavir.
An annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu.
CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as flu activity continues.
CDC issued Interim Guidance for Clinicians to Prioritize Antiviral Treatment of Influenza in the Setting of Reduced Availability of Oseltamivir through the Health Alert Network (HAN) on December 15, 2022.

U.S. Virologic Surveillance

Nationally and in all 10 HHS regions, the percentage of specimens testing positive for influenza in clinical laboratories declined ≥ 0.5% compared to the previous week. 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	86,499	2,033,784
No. of positive specimens (%)	2,588 (3.0%)	320,409 (15.8%)
*Positive specimens by type*
Influenza A	2,484 (96.0%)	318,141 (99.3%)
Influenza B	104 (4.0%)	2,268 (0.7%)

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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	5,727	147,926
No. of positive specimens	338	24,700
*Positive specimens by type/subtype*
Influenza A	329 (97.3%)	24,587 (99.5%)
(H1N1)pdm09	67 (26.8%)	4,746 (23.5%)
H3N2	183 (73.2%)	15,474 (76.5%)
H3N2v	0	1 (<0.1%)
Subtyping not performed	79	4,366
Influenza B	9 (2.7%)	113 (0.5%)
Yamagata lineage	0	0
Victoria lineage	2 (100%)	74 (100%)
Lineage not performed	7	39

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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 according to 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 genetically characterized 1,549 influenza viruses collected since October 2, 2022.

A/H1	530
		6B.1A	530 (100%)	5a.1	1 (0.2%)
				5a.2	529 (99.8%)
A/H3	994
		3C.2a1b	994 (100%)	1a	0
				1b	0
				2a	0
				2a.1	0
				2a.2	994 (100%)
		3C.3a	0	3a	0
B/Victoria	25
		V1A	25 (100%)	V1A	0
				V1A.1	0
				V1A.3	3 (12%)
				V1A.3a	0
				V1A.3a.1	0
				V1A.3a.2	22 (88%)
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 2022-2023 Northern Hemisphere recommended 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: Seventy-four A(H1N1)pdm09 viruses were antigenically characterized by HI, and 73 (99.9%) 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.
A (H3N2): One hundred and fifty-eight A(H3N2) viruses were antigenically characterized by HINT, and 147 (93%) were well-recognized (reacting at titers that were within 8-fold of the homologous virus titer) by ferret antisera to cell-grown A/Darwin/6/2021-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

Influenza B Viruses

B/Victoria: Ten influenza B/Victoria-lineage virus were antigenically characterized by HI, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown B/Austria/1359417/2021-like reference viruses representing the B/Victoria component for the cell- and recombinant-based influenza vaccines.
B/Yamagata: No influenza B/Yamagata-lineage viruses were available for antigenic characterization.

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 U.S. since October 2, 2022, were tested for antiviral susceptibility as follows:

Neuraminidase Inhibitors
Oseltamivir	Viruses Tested	1,593	546	1,020	27	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	1,593	546	1,020	27	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	1,593	546	1,020	27	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	1,548	524	997	27	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 respiratory illness referred to as 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 3, 2.6% 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 is a decline compared to what was reported in week 2 but remains above the national baseline of 2.5%. Six of the 10 HHS regions are below their respective baselines; region 7 is at their baseline; and regions 2, 3, and 9 are above their respective baselines. The percent of patient visits for respiratory illness decreased by > 0.1 percentage point for all regions during week 3 compared to week 2. 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.”

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Outpatient 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 decreased in the 25-49 years, 50-64 years, and 65+ years age groups and remained stable (change of ≤ 0.1 percentage point) in the 0-4 years and 5-24 years age groups in week 3 compared to week 2.

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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 3 (Week ending Jan. 21, 2023)	Week 2 (Week ending Jan. 14, 2022)	Week 3 (Week ending Jan. 21, 2023)	Week 2 (Week ending Jan. 14, 2022)
Very High	0	0	3	4
High	3	7	23	39
Moderate	7	7	50	66
Low	11	20	117	158
Minimal	33	21	470	419
Insufficient Data	1	0	266	243

*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 3, 240 (1.7%) of 14,330 reporting facilities reported at least one influenza positive test among their residents. This decreased by > 5% compared to week 2.

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Additional information about long-term care facility surveillance:
Surveillance Methods | Additional Data
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 13 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 17,001 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2022, and January 21, 2023. The weekly hospitalization rate observed in week 3 was 0.6 per 100,000 population. The weekly rate observed during week 48 (week ending December 3) is the third highest peak weekly rate observed during all seasons going back to 2010-2011; this follows the 2017-18 season which peaked during week 1 (week ending January 6, 2018) and the 2014-15 season which peaked during week 52 (week ending December 27, 2014).

The overall cumulative hospitalization rate was 58.1 per 100,000 population. This cumulative hospitalization rate is 1.4 times higher than the highest cumulative in-season hospitalization rate observed in week 3 during previous seasons going back to 2010-2011 (prior season rates ranged from 0.5 per 100,000 to 41.9 per 100,000). However, this in-season cumulative hospitalization rate is still lower than end-of-season hospitalization rates for all but 4 pre-COVID-19-pandemic seasons (2015-16, 2013-14, 2011-12, 2010-11 seasons).

When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (171.2). Among adults aged 65 and older, rates were highest among adults aged 85 and older (312.2). Among persons aged <65 years, hospitalization rates per 100,000 population were highest among children aged 0-4 years (78.1) followed by adults aged 50-64 years (61.7). When examining rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (81.2), followed by non-Hispanic American Indian or Alaska Native persons (69.9), non-Hispanic White persons (48), Hispanic/Latino persons (43.9), and non-Hispanic Asian/Pacific Islander persons (24.6).

Among 17,001 hospitalizations,16,485 (97%) were associated with influenza A virus, 295 (1.7%) with influenza B virus, 23 (0.1%) with influenza A virus and influenza B virus co-infection, and 198 (1.2%) with influenza virus for which the type was not determined. Among 3,369 hospitalizations with influenza A subtype information, 2,591 (76.9%) were A(H3N2), and 778 (23.1%) were A(H1N1)pdm09. Based on preliminary data, of the 2,809 laboratory-confirmed influenza-associated hospitalizations with more complete data, 3.4% (95% CI: 2.7%-4.1%) also tested positive for SARS-CoV-2.

Among 1,980 hospitalized adults with information on underlying medical conditions, 96.7% had at least one reported underlying medical condition, the most commonly reported were hypertension, cardiovascular disease, metabolic disorder, and obesity. Among 706 hospitalized women of childbearing age (15-49 years) with information on pregnancy status, 285 (40.4%) were pregnant. Among 688 hospitalized children with information on underlying medical conditions, 67.2% had at least one reported underlying medical condition; the most commonly reported was asthma, followed by neurologic disease and obesity.

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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 | RESP-NET Interactive
HHS Protect Hospitalization Surveillance

Hospitals report to HHS Protect the number of patients admitted with laboratory-confirmed influenza. During week 3, 4,009 patients with laboratory-confirmed influenza were admitted to a hospital. This was a decrease of > 5% compared to week 2.

View Chart Data | View Full Screen

Additional HHS Protect hospitalization surveillance information:
Surveillance Methods | Additional Data
Mortality Surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on January 26, 2023, 12.0% of the deaths that occurred during the week ending January 21, 2023 (week 3), were due to pneumonia, influenza, and/or COVID-19 (PIC). This percentage decreased (≥ 0.3 percentage point change) compared to week 2 and is above the epidemic threshold of 7.1% for this week. Among the 2,877 PIC deaths reported for this week, 1,332 had COVID-19 listed as an underlying or contributing cause of death on the death certificate, and 188 listed influenza. While current PIC mortality is due primarily to COVID-19, the proportion due to influenza increased from October through mid-December and has been decreasing for the past five weeks. 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

Six influenza-associated pediatric deaths occurring during the 2022-2023 season were reported to CDC during week 3. The deaths occurred between week 51 of 2022 (the week ending December 24, 2022) and week 3 of 2023 (the week ending January 21, 2023). All six deaths were associated with influenza A viruses. Four of the influenza A viruses had subtyping performed; one was a A(H1N1) virus and three were A(H3) viruses.

A total of 91 influenza-associated pediatric deaths occurring during the 2022-2023 season have been reported to CDC.

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Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Weekly U.S. Influenza Surveillance Report

https://www.cdc.gov/flu/weekly/index.htm

Learn more about the weekly influenza surveillance report (FluView) prepared by the Influenza Division.

No. of specimens tested	40,709	3,801,185
No. of positive specimens (%)	1,021 (2.5%)	137,999 (3.6%)
*Positive specimens by type*
Influenza A	969 (94.9%)	135,571 (98.2%)
Influenza B	52 (5.1%)	2,428 (1.8%)

Announcement

US FluView - Weekly Surveillance Flu report 2022/2023 season - for trend analysis

US FluView - Weekly Surveillance Flu report 2022/2023 season - for trend analysis

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