To evaluate the molecular evolutionary characteristics of influenza B virus hemagglutinin (HA) in Jiangsu Province.

Forty virus isolates in Jiangsu Province were selected between January 2010 and December 2012. The HA genes were amplified by two-step reverse transcription polymerase chain reaction (RT-PCR) approach, products were purified and sequenced by ABI 3730XL Genetic Analyzer. Surveillance data of influenza were extracted from China Information System for Disease Control and Prevention. Data were analyzed by SPSS, DNAStar, MEGA, BEAST softwares.

During January 2010 to December 2012, a total of 4 355 cases of influenza B were reported and confirmed, and 3 420 cases were identified as Victoria lineage and 935 belonged to the Yamagata lineage. Phylogenetic analysis of the HA sequences showed that the strains had higher homology in the same area and the same year. Compared with vaccine strain, HA1 of 28 strains of Victoria lineage occured antigen sites 146I→V, 197D→N, 129N→S and receptor binding site 197D→N substitutions and 197D→N substitution introduced a potential glycosylation site; the HA1 of Yamagata lineage strains had the antigen sites 198N→T, 116N→K, 146A→S receptor binding site 198N→T substitutions, and also introduced a glycosylation site at position 196. HAl gene of influenza B viruses seemed not to have been affected by positive selection. The mean evolutionary rate of HA1 gene was 1.05×10^-3 (95%HPD: 0.65×10^-3-1.45×10^-3 substitutions/(site·year). The results of Bayesian skyline plot model was consistence with the epidemiology data.

Some substitutions are found at HA1 antigen sites and receptor binding sites. Yamagata/Victoria lineage increase a potential glycosylation site at position 196/197, respectively.

Influenza B virus; Hemagglutinins; Evolution