Analysis on antigenic and genetic characteristics of influenza A(H1N1)pdm09 virus isolated in China, 2023

Objective To analyze the antigenic and genetic characteristics of influenza A（H1N1）pdm09 virus isolated in China in 2023.

Methods Antigenic analysis on 2 148 strains of influenza A（H1N1）pdm09 virus were performed by using hemagglutination inhibition test, and 505 of the strains were used for gene sequencing and analysis.

Results In the 2 148 strains of influenza A（H1N1）pdm09 virus tested in 2023, >95.00% shared similar antigenic characteristics with vaccine strains A/Victoria/4897/2022 and A/West Virginia/30/2022. And 98.42% （497/505） of sequenced strains had hemagglutinin （HA） gene belonging to clade C.1, in which there were multiple small subclades with common amino acid variations. Among the sequenced strains, 11 had known neuraminidase inhibitor resistance E119A, Q136K and H275Y substitutions.

Conclusion Influenza A（H1N1）pdm09 virus circulating in China in 2023 antigenically matched well with the vaccine strains, but the HA gene had varied genetic characteristics.