Assessment of Influenza Trends and Projected Vaccine Efficacy for the 2025-2026 Season

By
Eduardo Azziz-Baumgartner
Alicia Budd
Justin S. Lee
A. Danielle Iuliano
Sascha R. Ellington
Min Z. Levine
Xiao-yu Zheng
Larisa Gubareva
Katherine Adams
Jennifer DeCuir
Catherine H. Bozio
Carrie Reed
Marie K. Kirby
Benjamin Rambo-Martin
Jefferson M. Jones
Matthew Biggerstaff
Shikha Garg
Charles Todd Davis
Tom T. Shimabukuro
Erin Burns
Rebecca Kondor
Sonja J. Olsen
Vivien G. Dugan
VISION Coauthors
Stephanie A. Irving
Allison L. Naleway
Kristin Dascomb
Tamara Sheffield
Malini B. DeSilva
Sara Y. Tartof
Lina S. Sy
Nicola P. Klein
Ousseny Zerbo
Shaun J. Grannis
Brian E. Dixon
Melissa S. Stockwell
Ashley B. Stephens
Toan C. Ong
Michelle A. Barron
Sarah W. Ball
Zachary A. Weber
Emily L. Reeves
Caitlin S. Ray
June 17, 2026

Jama Network Open

Objective:

To provide US virologic, immunologic, and epidemiologic findings regarding influenza A(H3N2) viruses and vaccine effectiveness during the 2025-2026 season.

Approach:

Surveillance Activities: Systematic surveillance by the CDC identified mutations in the HA protein of influenza A(H3N2) viruses, raising concerns about vaccine-induced antibody evasion.
Data Collection: Data were collected from clinical and public health laboratories across the US, focusing on influenza virus types, subtypes, and clades.
Antigenic Characterization: Selected viruses underwent antigenic characterization using hemagglutination inhibition (HI) assays to assess similarity to vaccine reference viruses.
Vaccine Response Assessment: Sera samples from vaccinated individuals were analyzed for neutralizing antibody responses against circulating A(H3N2) viruses.
Hospitalization Surveillance: FluSurv-NET conducted population-based surveillance of laboratory-confirmed influenza hospitalizations, collecting detailed clinical data.
Genomic Sequencing: Whole-genome sequencing was performed on selected A(H3N2) isolates to identify genetic changes associated with antigenic drift.
Epidemiological Modeling: Models were developed to predict the impact of circulating strains on vaccine effectiveness and potential public health outcomes.

Key Findings:

Ten mutations in the HA protein of influenza A(H3N2) viruses were identified, indicating potential vaccine escape.
The emergence of subclade K viruses led to a protracted epidemic in Australia and an early severe season in Japan.
Antigenic drift was observed in circulating A(H3N2) viruses compared to the vaccine reference virus.

Interpretation:

The findings indicate significant changes in circulating influenza A(H3N2) viruses that may affect vaccine efficacy.

Limitations:

The study is based on data collected from specific regions and may not represent the entire US population.
Ethical considerations limited the scope of certain data collection methods.

Conclusion:

The study highlights the need for ongoing surveillance and assessment of influenza virus changes to inform vaccine development. ---

Sources:

CDC Influenza Surveillance

Assessment of Influenza Trends and Projected Vaccine Efficacy for the 2025-2026 Season

Objective:

Approach:

Key Findings:

Interpretation:

Limitations:

Conclusion:

Sources:

Original Source(s)

Influenza Activity and Estimated Vaccine Effectiveness During the 2025-2026 Influenza Season

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