ABSTRACT
@#Abstract: Objective To analysis the genetic evolution characteristics of hemagglutinin (HA) gene of influenza A(H1N1)pdm virus in Changsha City from 2016-2023, to understand the trend of the HA genetic evolution and the mutations of the amino acid. It provides a scientific basis for the prevention and control of influenza epidemics, as well as the screening of vaccines under the new situation. Methods The A(H1N1)pdm09 virus strains from Changsha City from 2016 to 2023 were isolated using SPF chicken embryos, and then the HA genes were sequenced by MiSeq of Illumina Inc. The homology of HA gene was analyzed by MegAlign of the DNASTAR, and the phylogenetic tree was constructed using the Neighbor Joining (NJ) method in the Molecular Evolutionary Genetics Analysis version 11 (MEGA11). Results The homology of the HA gene of A(H1N1)pdm virus in Changsha from 2016 to 2023 was between 94.8%-99.9%, with the HA gene homology decreasing annually. The homology between the isolated strains of A(H1N1)pdm09 in Changsha City from 2016 to 2023 and the WHO recommended vaccine strain ranged from 96.8% to 99.0%, indicating a relatively good match between the flu isolates and the recommended vaccine strain. The phylogenetic tree of the HA gene of the A(H1N1)pdm09 influenza virus in Changsha City showed that the HA gene evolved into several different branches within the 6B branch, and it had currently evolved to 6B.1A.5a.2a branch. Constant mutations had occurred at the amino acid sites of the four antigenic determinant clusters of HA protein. Currently, amino acid mutations had occurred at 15 antigenic sites within the four antigenic determinant clusters, and the newly emerged A186T antigen mutant site in the isolates from 2023 was worth recent notice. The receptor-binding sites are relatively conserved in loop 130, minor amino acid mutations occurred in loop 220, whether the amino acid mutation site in loop 190 is becoming more stable needs to be further monitored. Taking A/California/07/2009 (CY121680) as the reference strain, most of the A(H1N1) pdm09 isolates in Changsha was increased 162 NQTY glycosylation site and was decreased 276 NTTC glycosylation site, and the glycosylation mutations at these two sites have become more stable recently. Conclusions The HA genes of influenza A(H1N1)pdm virus in Changsha are constantly evolving and mutating, suggesting influenza surveillance should be strengthened continuously.