Weekly US Influenza Surveillance Report: Key Updates for Week 53, ending January 3, 2026 | FluView

This graph reflects the number of specimens determined to be positive for influenza viruses at the public health lab (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 information for current and past seasons:

Novel Influenza A Virus Infections

No new confirmed human infections with avian influenza A(H5) virus were reported to CDC this week. To date, person-to-person transmission of avian influenza A(H5) virus (H5 bird flu) has not been identified in the United States.

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 691 influenza viruses collected since September 28, 2025.

Influenza Virus Characterization from viruses collected in the U.S. from September 29, 2019

Virus Subtype or Lineage
Genetic Characterization

Total No. of
Subtype/Lineage
Tested
HA
Clade
Number (% of
subtype/lineage
tested)
HA
Subclade
Number (% of
subtype/lineage
tested)

A/H1
193

5a.2a
2 (1.0%)
C.1.9.3
2 (1.0%)

5a.2a.1
191 (99.0%)
D.3.1
95 (49.2%)

D.3.1.1
96 (49.7%)

A/H3
436

2a.3a.1
436 (100%)
J.2
2 (0.5%)

J.2.2
5 (1.1%)

J.2.3
20 (4.6%)

J.2.4
10 (2.3%)

K
399 (91.5%)

B/Victoria
62

3a.2
62 (100%)
C.3.1
39 (62.9%)

C.5.1
7 (11.3%)

C.5.6
7 (11.3%)

C.5.6.1
5 (8.1%)

C.5.7
4 (6.5%)

B/Yamagata
0

Y3
0
Y3
0

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. Circulating viruses with antigenic testing results that show titer differences greater than 4-fold by HI or equal to or greater than 8-fold by HINT) are considered “low reactors” or antigenically drifted compared to the vaccine virus. From the recent genetically characterized viruses, a subset is selected for antigenic characterization based on identified genetic changes in their 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: 47 A(H1N1)pdm09 viruses collected since September 28, 2025, were antigenically characterized by HI, and 46 (97.9%) were well-recognized (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera to cell-grown A/Wisconsin/67/2022-like reference viruses representing the A(H1N1)pdm09 component for the cell- and recombinant-based influenza vaccines.
• A(H3N2): 59 A(H3N2) viruses collected since September 28, 2025, were antigenically characterized by HI or HINT, and 3 (5.1%) 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: 12 influenza B/Victoria-lineage viruses collected since September 28, 2025, since were antigenically characterized by HI, and 8 (66.7%) 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 and Methods | CDC.

Viruses collected in the U.S. since September 28, 2025, were tested for antiviral susceptibility as follows:

Viruses collected in the U.S. tested for antiviral susceptibility

Antiviral Medication
Total Viruses
A/H1
A/H3
B/Victoria

Neuraminidase Inhibitors
Oseltamivir
Viruses Tested
676
193
423
60

Reduced Inhibition
0
0
0
0

Highly Reduced Inhibition
0
0
0
0

Peramivir
Viruses Tested
676
193
423
60

Reduced Inhibition
0
0
0
0

Highly Reduced Inhibition
0
0
0
0

Zanamivir
Viruses Tested
676
193
423
60

Reduced Inhibition
0
0
0
0

Highly Reduced Inhibition
0
0
0
0

PA Cap-Dependent Endonuclease Inhibitor
Baloxavir
Viruses Tested
656
180
416
60

Decreased Susceptibility
0
0
0
0

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 53, 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 week’s percentage decreased (change of > 0.1 percentage points) compared to Week 52 nationally, in HHS Regions 1 through 8, and in region 10 while the percentage in region 9 increased. The decrease could be due to changes in healthcare seeking or reporting during the holidays rather than an indication that influenza activity has peaked. Nationally and in all ten HHS regions, this week’s percentage is above 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.”

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 increased (change of > 0.1 percentage points) in the 65 years and older 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 in Week 53 compared to Week 52.

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).

ILI Activity by State/Jurisdiction and Core Based Statistical Area

Activity Level
Number of Jurisdictions
Number of CBSAs

Week 53
(Week ending
Jan. 3, 2025)
Week 52
(Week ending
Dec. 27, 2025)
Week 53
(Week ending
Jan. 3, 2025)
Week 52
(Week ending
Dec. 27, 2025)

Very High
27
34
113
136

High
17
15
228
223

Moderate
5
2
125
107

Low
3
3
126
136

Minimal
2
1
108
103

Insufficient Data
1
0
229
224

*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:

National Syndromic Surveillance System (NSSP)

The national percentage of emergency department (ED) visits with a discharge diagnosis (DD) of influenza reported in NSSP was 6.3% during Week 53 and decreased (change of > 0.1 percentage point) compared to the previous week. The percentage of ED visits with a DD of influenza decreased this week compared to the previous week among the 0-4 years, 5-17 years, and 18-64 years age group. The 65 years and older age group remained stable. The percentage of ED visits decreased in HHS regions 1-9 and remained stable in region 10. These decreases could be due to changes in healthcare seeking or reporting during the holidays rather than an indication that influenza activity has peaked.

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 14,153 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2025, and January 3, 2026. The weekly hospitalization rate observed during Week 53 was 8.7 per 100,000 population. The cumulative hospitalization rate observed in Week 53 was 40.6 per 100,000 population. This is the second highest cumulative rate at this time of the season since the 2010-11 season.

Among all hospitalizations, 13,732 (97.0%) were associated with influenza A virus, 318 (2.2%) with influenza B virus, 13 (0.1%) with influenza A virus and influenza B virus co-infection, and 90 (0.6%) with influenza virus for which the type was not determined. Among those with influenza A subtype information, 2627 (89.7%) were A(H3N2), and 303 (10.3%) 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 (130.7), followed by children aged 0-4 years (46.0), adults aged 50-64 years (35.6), children aged 5-17 years (19.3), and adults aged 18-49 years (16.0). Among children, rates are highest among infants aged less than 1 year (73.7), followed by children aged 1-4 years (39.2). For all pediatric age groups, this is the second highest cumulative rate at this time of the season since the 2010-11 season.

When examining age-adjusted rates by race and ethnicity, the highest rate of hospitalization per 100,000 population was among non-Hispanic Black persons (72.2), followed by American Indian or Alaska Native persons (38.1), Hispanic persons (34.8), non-Hispanic White persons (32.0), and Asian and/or Pacific Islander persons (16.6).

Additional FluSurv-NET data are available on FluView Interactive including hospitalization rates for the current and past seasons by age, sex, and race/ethnicity (http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html) as well as data on patient characteristics at: (http://gis.cdc.gov/grasp/fluview/FluHospChars.html.)

FluSurv-NET data are used to generate national estimates of the total numbers of influenza cases, medical visits, hospitalizations and deaths. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm.

**In this figure, weekly rates for all seasons prior to the 2024-2025 season reflect end-of-season rates. For the 2024-2025 season, rates for recent hospital admissions are subject to reporting delays and are shown as a dashed line for the current season. As hospitalization data are received each week, prior case counts and rates are updated accordingly.

Additional FluSurv-NET hospitalization surveillance information for current and past seasons and additional age groups:

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 53, 39,945 laboratory-confirmed influenza-associated hospitalizations were reported. This week’s influenza-associated hospital admission rate (11.8 per 100,000 population) increased (difference of ≥ 0.2) compared to Week 52.

Laboratory confirmed influenza-associated hospital admission rates per 100,000 population increased in HHS regions 1, 3, 5, 7, 8, 9, and 10, while regions 2 and 4 remained stable and region 6 decreased. Admission rates ranged from 4.3 (Region 9) to 18.1 (Region 1) during Week 53.

When examining rates by age for Week 53, the hospitalization rate among the 50-to-64 and the 65+ age groups increased (difference of ≥ 0.2), the 18-to-49 age group remained stable, and the 0-to-4 and 5-to-17 age groups decreased. The highest hospital admission rate per 100,000 population was among those 65 years and older (41.7), followed by children aged 0-4 years (11.2), and adults aged 50-64 years age groups (9.1).

Additional NHSN Hospital Respiratory Data information:

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 53, the hospitalization rate for residents with a positive influenza test in the prior 10 days was 54.1 per 100,000 residents. The national rate and rate for HHS regions 1, 2, 3, 4, 5, 9, and 10 have been trending upward over the past several weeks. In regions 6, 7, and 8 the rate does not show a consistent trend.

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

Mortality surveillance

National Center for Health Statistics (NCHS) Mortality Surveillance

Based on NCHS mortality surveillance data available on January 8, 2026, 1.9% of the deaths that occurred during the week ending January 3, 2026 (Week 53), were due to influenza. This percentage increased (≥ 0.1 percentage point change) compared to Week 52. The data presented are preliminary and may change as more data are received and processed.

Influenza-Associated Pediatric Mortality

Eight influenza-associated pediatric deaths occurring during the 2025-2026 season were reported to CDC during Week 53. The deaths occurred during weeks 51, 52 and 53 (the weeks ending December 20, 2025, December 27, 2025, and January 3, 2026). All the deaths were associated with influenza A viruses. Six of the influenza A viruses had subtyping performed and all were A(H3N2) viruses.

A total of 17 influenza-associated pediatric deaths occurring during the 2025–2026 season have been reported to CDC.

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