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National Influenza Activity:
• According to this week’s FluView report, seasonal influenza activity remains elevated across most of 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:
In the News:
First H5 Bird Flu Death Reported in United States | CDC Newsroom
Highly Pathogenic Avian Influenza A(H5N1) Virus Infections in Human - NEJM
Influenza Activity in the U.S.
Key Points:
• Although some indicators have decreased or remained stable this week compared to last, this could be due to changes in healthcare seeking or reporting during the holidays rather than an indication that influenza activity has peaked. The country is still experiencing elevated influenza activity and is expected to continue for several more weeks.
• During Week 1, of the 1,783 viruses reported by public health laboratories, 1,743 were influenza A and 40 were influenza B. Of the 1,403 influenza A viruses subtyped during Week 1, 625 (44.5%) were influenza A(H1N1)pdm09 and 778 (55.5%) were A(H3N2).
• 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. However, the first influenza A(H5)-associated death in the United States was reported by the Louisiana Department of Health in a case that was identified in mid-December.
• CDC estimates that there have been at least 9.1 million illnesses, 110,000 hospitalizations, and 4,700 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 January 4, 2025:
Viral Surveillance - Clinical Lab: The percentage of respiratory specimens testing positive for influenza at clinical laboratories is 18.6% 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 1 was 6.1% which is above baseline.
Outpatient Respiratory Illness: ILINet Activity Map: Five jurisdictions experienced moderate ILI activity and 43 jurisdictions experienced high or very high ILI activity in week 1.
Laboratory-Confirmed influenza Hospitalizations can be found here: Laboratory-Confirmed Influenza Hospitalizations (cdc.gov) The weekly hospitalization rate observed in Week 1 was 6.8 per 100,000 population. The cumulative hospitalization rate was 23.2 per 100,000 population.
NCHS Mortality: 1.1% of deaths were due to influenza. This percentage increased (> 0.1 percentage point change) compared to week 52. (NCHS:National Center for Health Statistics)
Influenza-Associated Pediatric Deaths: Five influenza-associated deaths were reported this week. Sixteen 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 1, 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.
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