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.