US Influenza Surveillance Report: Key Updates for Week 49, Dec 6, 2025
In the latest U.S. Influenza Surveillance Report for Week 49, ending December 6, 2025, influenza activity has been reported to rise across most regions of the country. The Centers for Disease Control and Prevention (CDC) highlighted significant trends in respiratory illness related to influenza and other viruses.
Key Highlights from the Influenza Surveillance Report
- Seasonal influenza activity has increased nationwide.
- Indicators of influenza positivity and related hospital visits have risen.
- The first pediatric death associated with influenza this season has been documented.
- Influenza A(H3N2) is currently the most prevalent strain circulating.
Influenza Virus Statistics for Week 49
During this week, 547 influenza viruses were reported by public health laboratories. Of these, 525 were classified as Influenza A and 22 as Influenza B. Specifically, 14% of subtyped Influenza A viruses were A(H1N1)pdm09, while a clear majority of 86% were A(H3N2).
Emerging Variants and Vaccine Effectiveness
A novel H3N2 subclade, identified as J.2.4.1 (renamed “H3N2 subclade K”), was flagged as having antigenic drift, potentially impacting vaccine effectiveness. The CDC encourages vaccination despite these mutations, as vaccination continues to provide substantial protection against severe illness and hospitalizations.
Overall Impact of Influenza
CDC estimates indicate there have been over 2.9 million influenza illnesses, approximately 30,000 hospitalizations, and around 1,200 deaths since the onset of the flu season. The total number of vaccine doses administered this season exceeds 127 million.
Regional Surveillance Data
Influenza positivity trends reveal that in regions 1, 3, and 8, positivity rates have notably increased. Region 8 displays the highest positivity at 20.8%, while Region 9 reports the lowest at 3.2%. Additionally, 94.2% of hospitalizations this season are linked to Influenza A.
| Indicator | Week 49 | Cumulative Since September 28, 2025 |
|---|---|---|
| No. of hospitalized patients | 2,415 | 6,884 |
| Percentage of ILI visits | 3.2% | Above national baseline |
| Deaths due to influenza | 0.2% of total deaths | New pediatric deaths reported |
Conclusion
The ongoing flu season has shown an increase in activity with prominent strains reported. Vaccination remains a critical tool in combating the flu, with the CDC urging everyone six months and older to get vaccinated. Continued monitoring and public health guidance will be essential as the season progresses.
