Influenza Activity in the U.S. Key Points: • Seasonal influenza (flu) activity continues to decline; however, CDC expects several more weeks of flu activity.
This season is classified as a high severity season overall and for all age groups (children, adults, older adults) and is the first high severity season since 2017-2018.
• During Week 13, of the 1,049 viruses reported by public health laboratories, 929 were influenza A and 120 were influenza B. Of the 806 influenza A viruses subtyped during Week 13, 448 (55.6%) were influenza A(H1N1)pdm09, 358 (44.4%) were A(H3N2), and 0 (0%) were A(H5).
• No new influenza A(H5) cases were reported to CDC this week. To date, human-to-human transmission of avian influenza A(H5) virus (H5 bird flu) has not been identified in the United States.
• CDC estimates that there have been at least 45 million illnesses, 580,000 hospitalizations, and 25,000 deaths from flu so far this season.
• CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as influenza viruses are circulating.
• 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 severe illness.
• 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.
Below is a summary of the key influenza indicators for the week ending March 29, 2025:
Viral Surveillance - Clinical Lab: The percentage of respiratory specimens testing positive for influenza at clinical laboratories is 9.7% this week.
Viral Surveillance - Public Health Lab: Influenza A(H1N1) pdm09, A(H3N2) and B viruses were co-circulating this week.
Virus Characterization: Influenza virus characterization information can be found here:
Influenza Virus Genome Sequencing and Genetic Characterization
Outpatient Illness: The percentage of patient visits to a health care provider for respiratory illness in week 13 was 3.2% which is above baseline.
Outpatient Respiratory Illness: ILINet Activity Map: Twelve jurisdictions experienced moderate ILI activity and 2 jurisdictions experienced high or very high ILI activity in week 13.
Laboratory-Confirmed influenza Hospitalizations can be found here: Laboratory-Confirmed Influenza Hospitalizations (cdc.gov) The weekly hospitalization rate observed in Week 13 was 1.4 per 100,000 population. The cumulative hospitalization rate was 121.9 per 100,000 population which is the highest cumulative hospitalization rate for Week 13 across all seasons since 2010-2011.
NCHS Mortality: 0.9% of deaths were due to influenza in week 13. This percentage decreased (> 0.1 percentage point change) compared to week 12. (NCHS:National Center for Health Statistics)
Influenza-Associated Pediatric Deaths: Nine influenza-associated deaths were reported this week. One hundred and sixty-eight pediatric deaths have been reported so far this season. For more information: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html
CDC FluView Site
https://www.cdc.gov/fluview/
Influenza Activity in Massachusetts
For more information about flu, please go to our Viral Respiratory Disease Dashboard which includes information not only on influenza but also other acute respiratory diseases, COVID-19, and respiratory syncytial virus (RSV), wastewater data and immunizations for respiratory diseases.
The figure below shows that for MMWR week 13, the percent of ILI visits in the current week is above the regional baseline of 1.9% but continues to decrease. (The CDC uses trends from past years to determine a region-specific baseline rate of ILI visits, which for Massachusetts is 1.9%. A rate above this regional baseline indicates higher than normal levels of ILI in the state.) For more information on how regional baselines are calculated see CDC’s influenza surveillance website at U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC) For more information on weekly flu activity, see CDC’s influenza surveillance website at https://www.cdc.gov/fluview/surveillance/index.html.
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ILI Activity in Massachusetts by Region - The map below shows the relative intensity of reported ILI activity in Massachusetts by region. Although regions may not all experience the same intensity of ILI at similar times, infections due to influenza can be found throughout Massachusetts during flu season. At this time, the Southeast region is experiencing high ILI activity. The West, Central, Northeast, and Outer Metro Boston regions are experiencing moderate ILI activity and the Boston and Inner Metro Boston regions are experiencing low ILI activity.
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