Highlights
?H1N1 strains were collected from Hunan and Jiangsu provinces in early 2023 following the optimized COVID-19 strategy.

?Phylogenic analysis revealed that the epidemic H1N1 viruses fell into different HA clades compared to vaccine strains.

?Mutations on HA antigenic sites suggest antigenic drift in the epidemic H1N1 viruses versus vaccine strains.

?A potential mismatch was found between recommended vaccine strains and the epidemic H1N1 viruses.

?The expeditious, precise, and personalized vaccine update program for influenza virus may need to be put on the agenda.