Weekly US Influenza Surveillance Report: Key Updates for Week 46, ending November 15, 2025

Summary

Viruses

Illness

All data are preliminary and may change as more reports are received.

Directional arrows indicate changes between the current week and the previous week. Additional information on the arrows can be found at the bottom of this page.

A description of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component is available on the surveillance methods page.¹

Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

U.S. virologic surveillance

Nationally and in HHS regions 1, 2, 4, 5, 6, 8, and 10, the percentage of respiratory specimens testing positive for influenza virus in clinical laboratories increased (change of ≥ 0.5 percentage points) compared to the previous week. In regions 3, 7, and 9, the percentage remained stable compared to the previous week but is trending upwards over the past several weeks. Percent positivity varied by region, ranging from 1.3% (Region 7) to 10.3% (Region 8). The Region 8 data are being driven by a pediatric hospital. 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.

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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 influenza viruses that belong to each influenza subtype/lineage.

_{*These data reflect specimens tested, and the number determined to be positive for influenza viruses at the public health labs (specimens tested is not the same as cases). The data do not reflect specimens tested only at CDC and 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"}

_{^†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 human-to-human.}

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Novel Influenza A Virus Infections

Two confirmed human infections with novel influenza A viruses were reported to CDC this week. One infection with an influenza A(H5N5) virus was reported by the Washington State Department of Health and one infection with an influenza A(H1N2) variant (A(H1N2)v) virus was reported by the Vermont Department of Health.

One infection with an influenza A(H5N5) virus was reported by the Washington State Department of Public Health. The case occurred in an individual aged ≥18 years. This individual developed symptoms during the week ending October 25, 2025 (Week 43) and was hospitalized with their illness during the week ending November 8, 2025 (Week 45). Respiratory specimens collected at the healthcare facility tested positive for influenza A and were presumptive positive for influenza A(H5) at the University of Washington. The specimens were sent to the Washington State Public Health Laboratory where influenza A(H5) was confirmed using the CDC influenza A(H5) assay. Sequencing conducted at the University of Washington and at the CDC indicated this was an influenza A(H5N5) virus. The investigation by public health officials identified that the patient kept backyard poultry that had exposure to wild birds. The patient remains hospitalized. This is the twelfth confirmed influenza A(H5) case in Washington overall. Prior confirmed cases in Washington were associated with commercial poultry exposure. This is the 71^st confirmed human case of A(H5) in the United States since early 2024 and the first human case reported in the United States since February 2025.

One infection with an influenza A(H1N2)v virus was reported by the Vermont Department of Health in an individual aged ≥18 years. The individual developed symptoms and sought healthcare during the week ending October 4, 2025 (Week 40), was hospitalized but discharged on the same day, and has recovered from their illness. The investigation conducted by state public health officials was unable to determine whether the individual had exposure to swine or other animals, or whether the patient's close contacts exhibited any illness. No human-to-human transmission has been identified associated with this case.

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.

Notification to WHO of the influenza A(H5) case was completed according to International Health Regulations (IHR). For the A(H1N2)v, this is the second of this subtype reported this calendar year. More information regarding IHR can be found at http://www.who.int/topics/international_health_regulations/en/.

The CSTE position statement, which includes updated case definitions for confirmed, probable, and suspected cases is available at http://www.cste.org/resource/resmgr/position_statements_files_2023/24-ID-09_Novel_Influenza_A.pdf.

An up-to-date human case summary during the current outbreak by state and exposure source is available at www.cdc.gov/bird-flu/situation-summary/index.html.

Information about avian influenza is available at https://www.cdc.gov/flu/avianflu/index.htm. A(H5N1) virus interim recommendations for Prevention, Monitoring, and Public Health Investigations are available at https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html.

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 558 influenza viruses collected since May 18, 2025.

CDC antigenically characterizes influenza viruses by hemagglutination inhibition (HI) assay (H1N1pdm09, H3N2, and B/Victoria viruses) or neutralization-based HINT (H3N2 viruses) using antisera from ferrets infected with reference viruses representing the recommended cell-based or recombinant influenza vaccines for the 2025-2026 Northern Hemisphere season. Antigenic differences between viruses are determined by comparing how well the antibodies raised against the vaccine reference viruses recognize the circulating viruses, which were 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 are deemed antigenically similar when their HI titer differences are less than or equal to 4-fold. In HINT, viruses with similar antigenic properties have antibody neutralization titer differences of less than 8-fold. From the recent genetically characterized viruses, a subset is selected for antigenic characterization based on identified genetic changes in surface proteins. The subset tested may not be proportional to the number of such viruses circulating in the United States.

Influenza A Viruses

• A(H1N1)pdm09: 127 A(H1N1)pdm09 viruses were antigenically characterized by HI, and 127 (100%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/67/2022-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines.
• A(H3N2): 50 A(H3N2) viruses were antigenically characterized by HI or HINT, and 19 (38.0%) 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/District Of Columbia/27/2023-like reference viruses representing the A(H3N2) component for the cell- and recombinant-based influenza vaccines.

Influenza B Viruses

• B/Victoria: 78 influenza B/Victoria-lineage virus were antigenically characterized by HI, and 54 (69.2%) 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 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 andMethods | CDC.

Viruses collected in the United States since May 18, 2025, were tested for antiviral susceptibility are as follows:

One A(H1N1)pdm09 virus had amino acid substitutions NA-I223V and NA-S247N and showed reduced inhibition by oseltamivir. One A(H1N1)pdm09 virus had PA-K34R amino acid substitution associated with reduced susceptibility to baloxavir.

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

Outpatient Respiratory Illness Visits

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 virus, SARS-CoV-2, and RSV. 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.

Nationally, during Week 46, 2.2% 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 week’s percentage is below the national baseline of 3.1% and remained stable (change of ≤ 0.1 percentage points) compared to Week 45 but has been trending upward slowly during the past several weeks. HHS Regions 6, 8, and 10 increased (change of > 0.1 percentage points), while regions 1, 2, 3, 4, 5, 7, and 9 remained stable (change of ≤ 0.1 percentage points) this week compared to the previous week. All 10 HHS 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.

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Outpatient Respiratory Illness Visits by Age Group

About 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. Based on these data, the percentage of visits for respiratory illness for the 0-4 years and 5-24 years age groups increased (change of > 0.1 percentage points) while the 25-49 years, 50-64 years, and 65 years and older age groups remained stable (change of ≤ 0.1 percentage point) in Week 46 compared to Week 45.

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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).

National Syndromic Surveillance System (NSSP)

The national percentage of emergency department (ED) visits with a discharge diagnosis (DD) of influenza reported in NSSP was 0.6% during Week 46 and increased (change of ≤ 0.1 percentage point) compared to the previous week. The percentage of ED visits with a DD of influenza increased this week compared to the previous week in the 0-4 years and 5-17 years age groups and remained stable in the 18-64 years and 65 years and older age groups. HHS regions 3, 6, and 8 increased this week compared to the previous week while all other regions remained stable.

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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 590 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2025 and November 15, 2025. The weekly hospitalization rate observed during Week 46 was 0.4 per 100,000 population. The cumulative hospitalization rate observed in Week 46 was 1.7 per 100,000 population.

Among all hospitalizations, 521 (88.3%) were associated with influenza A virus, 67 (11.4%) with influenza B virus, 2 (0.3%) with influenza A virus and influenza B virus co-infection, and 0 (0%) with influenza virus for which the type was not determined. Among those with influenza A subtype information, 68 (69.4%) were A(H3N2), and 30 (30.6%) 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 (5.1), followed by children aged 0-4 years (1.7), adults aged 50-64 years (1.6), children aged 5-17 years (1.0), and adults aged 18-49 years (0.7).

When examining age-adjusted rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (2.7), followed by Hispanic persons (1.6), American Indian or Alaska Native persons (1.4), non-Hispanic White persons (1.3), and Asian and/or Pacific Islander persons (1.2).

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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 46, 2,350 laboratory-confirmed influenza-associated hospitalizations were reported. This week's number of influenza-associated hospitalizations increased (change of ≥ 5%) slightly compared to Week 45.

Laboratory confirmed, influenza-associated hospital admission rates per 100,000 population remain low in all 10 HHS regions but have been trending upward over past several weeks and ranged from 0.3 (Region 10) to 1.2 (Region 2) during Week 46.

When examining rates by age for Week 46, all age groups remain low. The highest hospital admission rate per 100,000 population was among those 65 years and older (2.0), followed by 0-4 years (1.0), and 50-64 years age groups (0.5).

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National Healthcare Safety Network (NHSN) Long-Term Care Respiratory Pathogens & Vaccination Module

Long-term care facilities (LTCFs [e.g., Nursing homes/skilled nursing facilities]) report respiratory pathogen (e.g., COVID-19, influenza and RSV) data, including vaccination, cases, and hospitalizations among residents, to the NHSN Long-Term Care Respiratory Pathogens & Vaccination Module.

Nationally, during Week 46, the hospitalization rate for residents with a positive influenza test in the prior 10 days was 0.7 per 100,000 residents. The national rate and the rate in all 10 HHS regions remain low.

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Mortality surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

NCHS mortality surveillance data for the weeks ending October 4, 2025, through November 15, 2025 (Weeks 40 through 46) were not available for inclusion in this week's report. The following graph includes data through Week 39 of 2025 (the week ending September 27, 2025) and will be updated when data are available.

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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths occurring during the 2025-2026 season have been reported to CDC.

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All data in this report 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.¹

Additional information on the current and previous influenza seasons for each surveillance component are available on FluView Interactive.

Additional National and International Influenza Surveillance Information

Indicators Status by System

Additional surveillance information