Weekly US Influenza Surveillance Report: Key Updates for Week 42, ending October 24, 2026
For Everyone
Oct. 30, 2026, visit link for details.
What to know
Seasonal flu activity remains low nationally but is increasing in many parts of the country and is higher than typically observed at this time of year.
Summary
Viruses
7.6% (Trend )positive for influenzathis week.
The most frequently reportedinfluenza viruses this week were influenza A(H1N1)pdm09.
Illness
2.4% (Trend )of visits to a health care provider this week were for respiratory illness(below baseline).
2 moderate jurisdictions1 high or very high jurisdiction
Severe Disease
3.9cumulative hospitalization rateper 100,000 population
6,100 (Trend )patients admitted to hospitalswith influenza this week.
0.2% (Trend )of deaths attributed to influenza this week.
1influenza-associated death occurring during the 2026-27 season was 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
- Seasonal influenza activity remains low nationally, but multiple surveillance indicators have been increasing since late August/early September 2026.
- This early-season influenza activity is currently higher than typically observed at this time of year but an earlier increase in activity does not necessarily lead to a higher seasonal peak or greater overall severity.
- During Week 42 (the week ending October 24, 2026), of the 466 influenza viruses reported by public health laboratories, 456 were influenza A and 10 were influenza B. Of the 371 influenza A viruses subtyped during Week 42, 367 (98.9%) were influenza A(H1N1)pdm09 and 4 (1.1%) were A(H3N2).
- Since Week 21 (the week ending May 30, 2026), 82.7% of the influenza A viruses reported have been A(H1N1)pdm09 and among these, the majority have been D.3.1.1 HA subclade.
- The influenza A(H1N1) viruses detected this season are still A(H1N1)pdm09 viruses, which emerged in 2009 and have caused seasonal epidemics globally since then. Influenza viruses are constantly changing, often requiring updates to influenza vaccine viruses each season.
- Historically, influenza A(H1N1)pdm09 viruses have changed less often than A(H3N2) viruses. Recently circulating influenza A(H1N1)pdm09 viruses (which are in an HA subclade called "D.3.1.1") have divided into distinct groups with different genetic changes in their HA genes. We are seeing more genetic diversity among co-circulating A(H1N1)pdm09 viruses than we have before.
- It is too early to know what viruses may predominate or to say whether there might be implications on flu vaccine effectiveness this season.
- The first influenza-associated pediatric death occurring during the 2026-27 influenza season was reported to CDC this week.
- Because case investigation takes time, flu-associated deaths in children may be reported to CDC weeks after they occur; counts are preliminary and may increase. All reported cases meet the influenza-associated pediatric mortality case definition.
- CDC estimates in-season disease burden across all ages each week. CDC estimates that there have been at least 1,000,000 illnesses, 16,000 hospitalizations, and 900 deaths from flu so far this season.
- CDC's FluSight forecasts predict a likely increase nationally in both flu hospital admissions and the percentage of emergency department visits associated with flu for the week ending November 14, 2026. The number of new flu hospital admissions is forecast to range from 4,800 to 23,200 admissions, while the national percentage of emergency department visits due to flu is forecast to range from 1% to 4.4%.
- Annual seasonal influenza (flu) vaccination is recommended. Influenza vaccines are available for persons aged 6 months and older. People who are recommended for influenza vaccination but have not been vaccinated yet this season are encouraged to be vaccinated now.
- There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for patients at higher risk for influenza complications.1
- Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis.
U.S. Virologic Surveillance
Nationally, and in HHS regions 2, 3, 4, 5, 6, 7, 8, and 9, the percentage of respiratory specimens testing positive for influenza virus in clinical laboratories increased (change of at least 0.5 percentage points) compared to the previous week. In HHS regions 1 and 10, the percentage remained stable. A(H1N1)pdm09 viruses were the most frequently reported influenza viruses by public health laboratories this week. For regional and state level data and age group distribution, please visit
FluView Interactive. Viruses known to be associated with recent receipt of live attenuated influenza vaccine (LAIV) 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 virus) are used to monitor whether influenza activity is increasing or decreasing.
| Week 42 | Data Cumulative since
October 4, 2026
(Week 40) |
|---|
| No. of specimens tested | 53,102 | 171,495 |
| No. of positive specimens (%) | 4,061 (7.6%) | 10,359 (6.0%) |
| Positive specimens by type | | |
| Influenza A | 3,987 (98.2%) | 10,155 (98.0%) |
| Influenza B | 74 (1.8%) | 204 (2.0%) |
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 influenza viruses that belong to each influenza subtype.
| Week 42 | Data Cumulative since
October 4, 2026
(Week 40) |
|---|
| No. of specimens tested | 1,022 | 4,043 |
| No. of positive specimens | 466 | 1,835 |
| Positive specimens by type/subtype | | |
| Influenza A | 456 (97.9%) | 1,804 (98.3%) |
| Subtyping performed | 371 (81.4%) | 1,573 (87.2%) |
| (H1N1)pdm09 | 367 (98.9%) | 1,544 (98.2%) |
| H3N2 | 4 (1.1%) | 27 (1.7%) |
| H3N2v† | 0 | 0 |
| H5* | 0 | 2 (0.1%) |
| Subtyping not performed | 85 (18.6%) | 231 (12.8%) |
| Influenza B | 10 (2.1%) | 31 (1.7%) |
†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 person-to-person 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.
*These data reflect specimens tested, and the number determined to be positive for influenza viruses at the public health labs (specimens tested are not the same as human cases of A(H5) virus infection). If a specimen is only tested at CDC, it is not reflected in these data. The data could include more than one specimen tested per person. For more information on the number of people infected with A(H5) viruses, please visit the "
How CDC is monitoring influenza data among people to better understand the current avian influenza A (H5N1) situation"
This graph reflects the number of specimens determined to be positive for influenza viruses at the public health laboratory (specimens tested are not the same as cases). It does not reflect specimens tested only at CDC and could include more than one specimen tested per person. Specimens tested as part of routine influenza surveillance as well as those tested as part of targeted testing for people exposed to influenza A(H5) are included.
Additional virologic
Surveillance Methods | FluView Interactive:
National, Regional, and State Data or
Age Data
Novel Influenza A Virus Infections
No new confirmed human infections with a novel influenza virus were reported to CDC as of October 24, 2026.
Novel influenza A virus infections include human infections with influenza A viruses that are different from currently circulating human seasonal influenza A(H1) and A(H3) viruses or avian influenza A viruses that have sporadically infected people.
An up-to-date human case summary during the 2024 outbreak by state and exposure source is available at
www.cdc.gov/bird-flu/situation-summary/index.html.
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 relative to the reference viruses representing 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 polymerase acidic protein (PA) endonuclease inhibitor baloxavir. The HA clade and subclades were assigned using Nextclade (
https://clades.nextstrain.org).
CDC has genetically characterized 542 influenza viruses collected since May 24, 2026
Virus Subtype or
Lineage | Genetic Characterization | | | | |
|---|
Total No. of Subtype/
Lineage Characterized | HA Clade | Number (% of subtype/
lineage Characterized) | HA Subclade | Number (% of subtype/lineage Characterized) | |
|---|
| A(H1N1)pdm09 | 355 | | | | |
| | 5a.2a.1 | 355 (100%) | D.3.1 | 1 (0.3%) |
| D.3.1.1 | 354 (99.7%) | | | | |
| A(H3N2) | 97 | | | | |
| | 2a.3a.1 | 97 (100%) | J.2.4.2 | 5 (5.2%) |
| K | 92 (94.8%) | | | | |
| B/Victoria | 90 | | | | |
| | 3a.2 | 90 (100%) | C.3.1 | 39 (43.3%) |
| C.3.3 | 1 (1.1%) | | | | |
| C.5.1 | 2 (2.2%) | | | | |
| C.5.6 | 7 (7.8%) | | | | |
| C.5.6.1 | 41 (45.6%) | | | | |
Genetic Characterization of Hemagglutinin Genes from Influenza Viruses Collected since May 24, 2026
Genetic characterization of hemagglutinin (HA) genes from influenza A(H1N1)pdm09 viruses collected since May 24, 2026Monthly virus sequence counts and HA subclade proportions
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CDC
antigenically characterizes influenza viruses by
hemagglutination inhibition (HI) assay (H1N1pdm09, H3N2, and B/Victoria viruses) or neutralization-based
HINT (H3N2 viruses) using antisera that ferrets make after being infected with reference viruses representing the 2026-2027 Northern Hemisphere recommended cell-, recombinant- and nucleic acid-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 of the recent genetically characterized viruses and are chosen based on the genetic changes in their surface proteins and may not be proportional to the number of such viruses circulating in the United States.
Influenza A Viruses
- A(H1N1)pdm09:103 A(H1N1)pdm09 viruses were antigenically characterized by HI, and 97 (94.2%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Missouri/11/2025-like reference viruses representing the A(H1N1)pdm09 component for the cell-, recombinant- and nucleic acid-based influenza vaccines.
- A(H3N2): 22 A(H3N2) viruses were antigenically characterized by HI or HINT, and all were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer in HI or reacting at titers that were less than 8-fold of the homologous virus in HINT) by ferret antisera to cell-grown A/Darwin/1415/2025-like reference viruses representing the A(H3N2) component for the cell-, recombinant- and nucleic acid-based influenza vaccines.
Influenza B Viruses
- B/Victoria: 33 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/Pennsylvania/14/2025-like reference viruses representing the B/Victoria component for the cell-, recombinant- and nucleic acid-based influenza vaccines.
Assessment of Virus Susceptibility to Antiviral Medications
CDC assesses susceptibility of influenza viruses to the antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir using next generation sequence analysis supplemented by laboratory assays. Information about antiviral susceptibility test methods can be found at
U.S. Influenza Surveillance: Purpose and Methods | CDC.
Viruses collected in the U.S. since May 24, 2026, were tested for antiviral susceptibility as follows:
| Antiviral Medication | Total Viruses | A/H1 | A/H3 | B/Victoria |
|---|
| Neuraminidase Inhibitors | | | | |
| Oseltamivir | | | | |
| Viruses Tested | 537 | 354 | 96 | 87 |
| Reduced Inhibition | 8 (1.5%) | 8 (2.3%) | 0 | 0 |
| Highly Reduced Inhibition | 0 | 0 | 0 | 0 |
| Peramivir | | | | |
| Viruses Tested | 537 | 354 | 96 | 87 |
| Reduced Inhibition | 0 | 0 | 0 | 0 |
| Highly Reduced Inhibition | 0 | 0 | 0 | 0 |
| Zanamivir | | | | |
| Viruses Tested | 537 | 354 | 96 | 87 |
| Reduced Inhibition | 0 | 0 | 0 | 0 |
| Highly Reduced Inhibition | 0 | 0 | 0 | 0 |
| PA Cap-Dependent Endonuclease Inhibitor | | | | |
| Baloxavir | | | | |
| Viruses Tested | 509 | 330 | 90 | 89 |
| Decreased Susceptibility | 0 | 0 | 0 | 0 |
Eight A(H1N1)pdm09 viruses had amino acid substitutions NA-I223V and NA-S247N and showed reduced inhibition by oseltamivir.
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, use of these antivirals for treatment and prevention of influenza A virus infection is not recommended and data from adamantane resistance testing are not presented.
Outpatient and Emergency Department Illness Surveillance
ILINet
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient and emergency department visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and can therefore capture respiratory illness visits due to infection with any pathogen that can present with similar symptoms. 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 picture.
Nationally, during Week 42, 2.4% of patient visits reported through ILINet were due to ILI. This week's national percentage increased (change of > 0.1 percentage points) compared to Week 41 but remains below the national baseline of 2.9%. ILI activity increased in HHS regions 1, 2, 4, 6, 9 and 10 and remained stable (change of ≤ 0.1 percentage points) in regions 3, 5, 7, and 8 compared to Week 41. Region 10 is above its baseline, while all other regions are below their respective baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
*Some calendar years do not include an epidemiologic Week 53. In those years, the Week 53 value shown is the average between Week 52 and Week 1.
**Effective October 3, 2021 (Week 40), the respiratory illness definition (fever plus cough or sore throat) no longer includes "without a known cause other than influenza."
The percentage of visits for respiratory illness increased (change of > 0.1 percentage points) in the 0-4 years, 5-24 years 25-49 years, and 50-64 years age groups and remained stable (change of ≤ 0.1 percentage points) in the 65 years and older age groups this week compared to the previous week.
ILI 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. 24, 2026) | Week 41
(Week ending
Oct. 17, 2026) | Week 42
(Week ending
Oct. 24, 2026) | Week 41
(Week ending
Oct. 17, 2026) | |
| Activity Level | Number of Jurisdictions | Number of CBSAs | | |
|---|
| Very High | 0 | 0 | 0 | 0 |
| High | 1 | 0 | 9 | 1 |
| Moderate | 2 | 2 | 25 | 25 |
| Low | 10 | 5 | 82 | 67 |
| Minimal | 41 | 48 | 609 | 637 |
| Insufficient Data | 1 | 0 | 204 | 199 |
*Data collected in ILINet may disproportionally represent certain populations within a jurisdiction or CBSA, and therefore, may not accurately depict the full picture of respiratory virus 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
National Syndromic Surveillance System (NSSP)
The national percentage of emergency department (ED) visits with a discharge diagnosis (DD) of influenza reported in NSSP was 1.2% during Week 42 and increased (change of > 0.1 percentage point) compared to the previous week. Nationally, the percentage of ED visits with a DD of influenza increased among the 0-4 years, 5-17 years, and 18-64 years age groups and remained stable (change of ≤ 0.1 percentage point) among the 65 years and older age group. The percentage of ED visits with a DD of influenza increased this week compared to the previous week in HHS regions 4, 6, 8, 9, and 10, and remained stable in all other regions (1, 2, 3, 5, and 7). The age group trends varied by region, but most regions reported a pattern similar to the national data.
RegionNationalRegion 1Region 2Region 3Region 4Region 5Region 6Region 7Region 8Region 9Region 10
Season
2026-2027x
2025-2026x
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Additional information about emergency department visits for flu for current and past seasons:
Surveillance Methods |
Emergency Department Visits for COVID-19, flu, and RSV
Hospitalization Surveillance
FluSurv-NET
The
Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 10% 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 1,474 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 4, 2026, and October 24, 2026. The weekly hospitalization rate observed during Week 42 was 1.3 per 100,000 population. After accounting for reporting delays, the estimated rate during Week 42 likely ranges from 1.9 to 2.5. Estimated weekly rates are low but continue to increase; this is the highest weekly rate for Week 42 since the 2010-11 season. The cumulative hospitalization rate observed in Week 42 was 3.9 per 100,000 population.
Among all hospitalizations, 1,443 (97.8%) were associated with influenza A virus, 31 (2.1%) with influenza B virus, 0 with influenza A virus and influenza B virus co-infection, and 2 (0.1%) with influenza virus for which the type was not determined. Among those with influenza A subtype information, 2 (0.9%) were A(H3N2), and 223 (99.1%) were A(H1N1)pdm09.
When examining rates by age, the highest rate of hospitalization per 100,000 population was among adults aged 65 and older (13.3), followed by adults aged 50-64 years (4.2), children aged 0-4 years (3.2), adults aged 18-49 years (1.2), and children aged 5-17 years (1.0).
When examining age-adjusted rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (6.0), followed by Asian and/or Pacific Islander persons (4.7), American Indian or Alaska Native persons (4.2), Hispanic persons (3.5), and non-Hispanic White persons (3.1).
Additional FluSurv-NET information for current and past seasons:
Surveillance Methods | FluView Interactive:
Rates by Age, Sex, and Race/Ethnicity or
Data on Patient Characteristics
National Healthcare Safety Network (NHSN) Hospital Respiratory Data
Hospitals report to NHSN the weekly number of patients with laboratory-confirmed influenza who were admitted to the hospital. Nationally, during Week 42, 6,100 laboratory-confirmed influenza-associated hospitalizations were reported. This week's influenza-associated hospital admission rate (1.8 per 100,000 population) increased (difference of ≥ 0.25) compared to Week 41.
Laboratory-confirmed influenza-associated hospital admission rates per 100,000 population increased in HHS regions 2, 4, 5, 6, and 9 and remained stable in all other regions this week compared to the previous week. Regional admission rates during Week 42 ranged from 0.7 (Region 7) to 2.5 (Region 9).
When examining rates by age for Week 42, the 65 years and older age group increased (difference of ≥ 0.25) and all other age groups (0-4 years, 5-17 years, 18-49 years, and the 50-64 years) remained stable (difference of < 0.25) compared to the previous week. The highest hospital admission rate per 100,000 population was among those 65 years and older (5.8), followed by the 0-4 years age group (1.8) and the 50-64 years age group (1.6).
Additional NHSN Hospital Respiratory Data Module information
Surveillance Methods |
Additional Data |
FluView Interactive
Mortality Surveillance
National Center for Health Statistics (NCHS)
Based on NCHS mortality surveillance data available on October 29, 2026, 0.2% of the deaths that occurred during the week ending October 24, 2026 (Week 42) were due to influenza. This percentage remained stable (< 0.1 percentage point change) compared to Week 41 but is trending upward. The data presented are preliminary and may change as more data are received and processed.
Additional mortality surveillance information for current and past seasons (including pneumonia, influenza, and COVID-19):
Surveillance Methods |
FluView Interactive
Influenza-Associated Pediatric Mortality
Two influenza-associated pediatric deaths were reported to CDC during Week 42.
One death occurred during Week 40 (the week ending October 10, 2026) and was associated with an influenza A(H1N1) virus. This is the first influenza-associated pediatric death occurring during the 2026-2027 season that has been reported to CDC.
One death occurring during the 2025-2026 season was also reported, which brings the total number of pediatric deaths for last season to 199. This death was associated with an influenza B virus with no lineage determined and occurred during Week 37 of 2026 (the week ending September 19, 2026).
For surveillance purposes, an influenza-associated pediatric death is
defined as a death in a person less than 18 years of age, resulting from a clinically compatible illness that was confirmed to be influenza by an appropriate laboratory diagnostic test. There should be no period of complete recovery between the illness and death.
The data presented are preliminary and may increase as additional cases are identified and reported to CDC.
Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods |
FluView Interactive
Seasonal flu activity remains low nationally but is increasing in many parts of the country.
www.cdc.gov
