Genetic mutations in influenza H3N2 viruses from a 2012 epidemic in Southern China

Background An influenza H3N2 epidemic occurred throughout Southern China in 2012. Methods We analyzed the hemagglutinin (HA) and neuraminidase (NA) genes of influenza H3N2 strains isolated between 2011–2012 from Guangdong. Mutation sites, evolutionary selection, antigenic sites, and N-glycosylation within these strains were analyzed. Results The 2011–2012 Guangdong strains contained the HA-A214S, HA-V239I, HA-N328S, NA-L81P, and NA-D93G mutations, similar to those seen in the A/ Perth/16/2009 influenza strain. The HA-NSS 061–063 and NNS 160–162 glycosylation sites were prevalent among the 2011–2012 Guangdong strains but the NA-NRS 402–404 site was deleted. Antigenically, there was a four-fold difference between A/Perth/16/2009 -like strains and the 2011–2012 Guangdong strains. Conclusion Antigenic drift of the H3N2 subtype contributed to the occurrence of the Southern China influenza epidemic of 2012.