National Influenza Activity:
• According to this week’s FluView report, seasonal influenza activity remains elevated and continues to increase across the country.
• CDC continues to provide updated information and materials on the current HPAI A (H5N1) situation. The webpage can be viewed here.
• Updated preliminary estimates for 2024-2025 flu season burden and severity:
Preliminary Estimated Flu Disease Burden 2024-2025 Flu Season | Flu Burden | CDC
· 2024-2025 United States Flu Season: Preliminary In-Season Severity Assessment | Influenza (Flu) | CDC
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Influenza Activity in the U.S.
Key Points:
• During Week 5, of the 4,377 viruses reported by public health laboratories, 4,264 were influenza A and 113 were influenza B. Of the 3,458 influenza A viruses subtyped during Week 5, 1,857 (53.7%) were influenza A(H1N1)pdm09, 1,601 (46.3%) were A(H3N2), and 0 were A(H5).
• One human infection with an influenza A(H1N2) variant (A(H1N2)v) virus was reported.
• No new influenza A(H5) cases were reported to CDC this week. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States.
• CDC estimates that there have been at least 24 million illnesses, 310,000 hospitalizations, and 13,000 deaths from flu so far this season.
• CDC recommends that everyone ages 6 months and older get an annual influenza (flu) vaccine.
• There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for higher risk patients.
• 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 February 1, 2025:
Viral Surveillance - Clinical Lab: The percentage of respiratory specimens testing positive for influenza at clinical laboratories is 31.6% this week.
Viral Surveillance - Public Health Lab: Influenza A(H1N1)pdm09 and A(H3N2) were the predominant viruses reported this week.
Virus Characterization: Influenza virus characterization information can be found here: U.S. Influenza Surveillance: Purpose and Methods | CDC
Outpatient Illness: The percentage of patient visits to a health care provider for respiratory illness in week 5 was 7.8% which is above baseline.
Outpatient Respiratory Illness: ILINet Activity Map: Two jurisdictions experienced moderate ILI activity and 45 jurisdictions experienced high or very high ILI activity in week 5.
Laboratory-Confirmed influenza Hospitalizations can be found here: Laboratory-Confirmed Influenza Hospitalizations (cdc.gov) The weekly hospitalization rate observed in Week 5 was 9.2 per 100,000 population. The cumulative hospitalization rate was 64.0 per 100,000 population.
NCHS Mortality: 2.0% of deaths were due to influenza. This percentage increased (> 0.1 percentage point change) compared to week 4. (NCHS:National Center for Health Statistics)
Influenza-Associated Pediatric Deaths: Ten influenza-associated deaths were reported this week. Fifty-seven pediatric deaths have been reported so far this season. For more information: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html
CDC Flu View 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 5, the percent of ILI visits in the current week is above the regional baseline of 1.9%. (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. |
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, all regions (West, Central, Northeast, Southeast, Outer Metro Boston, Inner Metro Boston and Boston) are experiencing very high ILI activity.
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