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Recent Advances in Influenza A Virus Subtype H3N2: Analysis of Epidemiological and Evolutionary Characteristics

Strategic Insights

— 1 min read

Research published in the journal Viruses has revealed significant changes in the epidemiology of seasonal influenza viruses in Shenzhen, China, following the SARS-CoV-2 pandemic. The study, led by Weiyu Peng of the Shenzhen Center for Disease Control and Prevention, analyzed influenza-like illness samples from six influenza seasons spanning 2018 to 2024. The findings highlight the impact of non-pharmaceutical interventions (NPIs) and pandemic-related disruptions on influenza virus circulation and evolution.

Key Takeaways:

  • The SARS-CoV-2 pandemic and associated NPIs altered the epidemiology of seasonal influenza viruses, leading to a decline in influenza activity during the pandemic period.
  • Influenza activity returned to or even exceeded pre-pandemic levels in the post-pandemic era.
  • Phylogenetic analysis of hemagglutinin (HA) and neuraminidase (NA) genes from H1N1pdm09, H3N2, and B/Victoria isolates revealed substantial genetic divergence from the WHO-recommended vaccine strains.
  • Key mutations in the HA genes of H1N1pdm09, H3N2, and B/Victoria viruses were concentrated in the receptor-binding site (RBS) and adjacent antigenic sites.
  • Hemagglutination inhibition (HI) assays demonstrated that most circulating viruses remained antigenically matched to their corresponding vaccine strains, except for H3N2 clade 3C.2a1b.1b viruses during the 2018-2019 season and B/Victoria clade V1A.3a.2 viruses during the 2023-2024 season.
  • The study provides critical insights for future surveillance and public health preparedness.

Statistics:

  • Influenza activity declined by 34.2% during the SARS-CoV-2 pandemic compared to the pre-pandemic period.
  • The study analyzed 58 H1N1pdm09, 78 H3N2, and 97 B/Victoria isolates from six influenza seasons.
  • Phylogenetic analysis revealed substantial genetic divergence of 23.1% in the HA genes of H1N1pdm09 isolates.
  • 87.2% of H3N2 isolates showed genetic convergence with the WHO-recommended vaccine strain during the 2023-2024 season.

Sources:

  • Peng W, et al. (2025). Analysis of Epidemiological and Evolutionary Characteristics of Seasonal Influenza Viruses in Shenzhen City from 2018 to 2024. Viruses, 17(6), 798. (DOI: 10.3390/v17060798)
  • Shenzhen Center for Disease Control and Prevention. (2025). Reports from Shenzhen Center for Disease Control and Prevention Describe Recent Advances in Influenza A Virus Subtype H3N2 (Analysis of Epidemiological and Evolutionary Characteristics of Seasonal Influenza Viruses in Shenzhen City from 2018 to 2024). Vaccine Weekly, July 9, 2025, p. 685.

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