Flu Vaccine Cut Hospitalizations Despite Drifted H3N2 Strain

Interim CDC estimates found the 2025–2026 vaccine reduced outpatient influenza visits by up to 41% and hospitalizations by up to 41%.

By
Kerri Miller
March 17, 2026
5 min

MDSpire News

Objective:

To assess the effectiveness of the 2025–2026 seasonal influenza vaccine in reducing outpatient visits and hospitalizations due to influenza during the specified season.

Approach:

Key Findings:

Vaccine reduced outpatient visits by 22% to 34% and hospitalizations by 30% among adults, while pediatric patients showed the strongest protection with 38% to 41% effectiveness.
Vaccine effectiveness against influenza A(H3N2) was 35% for outpatient visits and 38% for hospitalizations in adults.
Influenza B showed higher outpatient effectiveness estimates of 71% and 45% in different networks.

Interpretation:

Despite antigenic drift in circulating viruses, the vaccine effectively reduced influenza-related morbidity, particularly in pediatric populations, highlighting the need for continued vaccination efforts.

Limitations:

Preliminary results may change as the season progresses.
Unmeasured confounding factors were not modeled, which may affect results.
Potential misclassification of vaccination status could impact effectiveness estimates.
Limited sample sizes in certain strata affected estimates.

Conclusion:

Vaccination significantly reduced the risk of influenza-associated outpatient visits and hospitalizations, underscoring the importance of influenza vaccination for all eligible individuals, especially in light of antigenic drift.