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Influenza caused by Influenza A virus subtype H3N2

Last edited: 4/10/2026

Overview

Influenza A virus subtype H3N2 is a strain of seasonal influenza that circulates among humans. While generally causing illness similar to other seasonal influenza strains, specific subtypes can vary in their impact and the effectiveness of available vaccines.

Diagnosis

Management

  • Development of mRNA-based influenza vaccines is ongoing, with one investigational vaccine (mRNA-1010) demonstrating acceptable safety and immunogenicity in adults 1.
  • The investigational mRNA-1010 vaccine showed higher immune responses against influenza A strains compared to influenza B strains 1.
  • Hemagglutination inhibition (HAI) titers are supported as a surrogate endpoint for evaluating influenza vaccine efficacy, similar to licensed vaccines 1.

    • Special Populations

    Key Recommendations

  • Further optimization and development of mRNA-1010 against seasonal influenza are supported by phase 3 trial findings 1. (Evidence: Moderate)
  • HAI titers can be used as a correlate of protection and a surrogate endpoint for evaluating mRNA-1010 vaccine efficacy 1. (Evidence: Moderate)

    • References

    1 Kandinov B, Soens M, Huang W, Llapur C, Ensz D, Essink B et al.. An mRNA-based seasonal influenza vaccine in adults: Results of two phase 3 randomized clinical trials and correlate of protection analysis of hemagglutination inhibition titers. Human vaccines & immunotherapeutics 2025. link 2 Qi Y, Guo W, Liu C, Li W, Gu Y, Li S et al.. Seroprevalence of influenza A (H9N2) virus infection among humans in China: A meta-analysis. Microbial pathogenesis 2021. link

    Original source

    1. [1]
      An mRNA-based seasonal influenza vaccine in adults: Results of two phase 3 randomized clinical trials and correlate of protection analysis of hemagglutination inhibition titers. — Kandinov B, Soens M, Huang W, Llapur C, Ensz D, Essink B et al. Human vaccines & immunotherapeutics (2025)
    2. [2]
      Seroprevalence of influenza A (H9N2) virus infection among humans in China: A meta-analysis. — Qi Y, Guo W, Liu C, Li W, Gu Y, Li S et al. Microbial pathogenesis (2021)
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