Genetic characterization of influenza A and B viruses circulating from 2017 to 2023 In Guizhou Province,China

Purpose This study analyzed the genetic characteristics of influenza viruses circulating in Guizhou Province from 2017 to 2023 and their match with seasonal vaccine strains. Methods Based on hemagglutinin (HA) gene sequences, we performed phylogenetic analysis and assessed amino acid homology, antigenic site, and glycosylation site variations in A(H1N1), A(H3N2), B Victoria (BV), and B Yamagata (BY) viruses. Results HA homology with vaccine strains was highly conserved for H1N1, BV, and BY (median > 98.7%). In contrast, H3N2 viruses showed significantly lower homology (median 98.0%; IQR 97.81%–98.00%) and broader variation (96.55%–99.09%). Phylogenetically, all H1N1 strains clustered within 6B.1A, H3N2 within 3C.2a1b, BV within 1A.3a.1, and BY within Y3. Notably, some H3N2 strains with low homology formed an independent cluster and commonly carried the S193F substitution in antigenic site B, suggesting potential antigenic drift. Key mutations in antigenic and glycosylation sites were identified across all subtypes, particularly in H3N2 and BV. Conclusion Despite overall high homology, the observed genetic variability—especially the emergence of a distinct H3N2 cluster with antigenic site mutations—highlights the continuous evolutionary potential of influenza viruses in Guizhou. These findings underscore the need for enhanced genomic surveillance to monitor antigenic drift, inform the timely reformulation of annual vaccine compositions, and support evidence-based recommendations on seasonal influenza vaccination.