Overview
- Interim national estimates show adult vaccine effectiveness of roughly 22%–34% against outpatient visits and about 30%–31% against hospitalization, with pediatric estimates at 38%–41% for outpatient care and 41% for hospitalization.
- Surveillance indicates 88% of subtyped influenza A viruses are H3N2 and 93% of those are an antigenically drifted subclade K distinct from the 2025–2026 vaccine virus.
- California’s parallel analysis of 952,765 tests found overall adjusted effectiveness of 33%, peaking at 39% in ages 6 months–17 years and dropping to 22% in adults 65 and older.
- Effectiveness varied by vaccine type: among eligible children it reached 55% with live attenuated vaccine versus 39% with standard-dose inactivated, and among adults 65+ it was 39% for recombinant, 22% for adjuvanted/high-dose, and 16% for standard-dose inactivated vaccines.
- CDC continues to recommend annual flu vaccination as fewer than half of children (48%) and adults (47%) were vaccinated by late February, with authors noting these findings are preliminary and subject to revision.