Analysis of influenza A( H3N2) subtype epidemic characteristics and HA1 gene characteristics in Ningbo in 2012

Objective To understand the epidemic characteristics of influenza A( H3N2) virus and study the HA1 gene variation situation in Ningbo city in 2012. Methods The specimens were collected from suspected cases in sentinel hospital weekly during 2012 to isolate influenza A( H3N2) subtype virus. Then the amino acid sequences were deduced and the HA1 gene characteristics were analyzed according to the nt sequence determination in HAl domain of hemagglutinin gene. Results The phylogenetic tree analysis showed that the influenza A( H3N2) virus isolates in Ningbo in 2012 and the representative strains in recent years were not in the same genetic branch. More than 8 amino acid sites in HA1 domain showed difference between the influenza A( H3N2) strains in 2012 and the representative strains in 2011,and the difference of 5 amino acid sites was also found when comparied with the vaccine strain in 2012-2013. Conclusion Large variation of H3N2 strains of influenza A virus was found in HA1 gene in 2012 in Ningbo,indicating that the H3N2 strains of influenza A virus mutates frequently in recent years.