Antigenic and genetic characteristics of influenza B virus in the mainland of China,2012- 2013

Objective To understand the epidemiological characteristics of influenza B and the antigenic and genetic characteristics of influenza B virus in the mainland of China during 2012-2013.Methods The antigenic characteristics of influenza B virus was analyzed with reference ferret anti-sera.The nucleotide sequences of the influenza B viruses were determined by Sanger dideoxy sequencing.The phylogenetic trees were constructed by neighbor-jointing method,the genetic characteristics were determined and compared the circulating influenza B virus with current vaccine strains.Results During 2012- 2013 influenza season influenza B virus accounted for 9.93%of total influenza viruses detected,the activity of B Victoria lineage virus were stronger than B Yamagata lineage virus.Most B Victoria lineage viruses had close antigenic relation with the vaccine strain B/Brisbane/60/2008(83.5%) recommended by WHO in previous year and the representative circulating strain B/Chongqing-Yuzhong/1384/2010(94.7%) in the mainland of China.The majority of B Yamagata lineage viruses had closely antigenic relation with WHO recommended vaccine strain B/Wisconsin/01/2010(99.3%) and WHO vaccine seed B/Hubei-Wujiagang/158/2009(98.0%);phylogenetic analysis on B Victoria lineage viruses indicated that one strain had intra-clade reassortants between HA and NA gene.One of the B Yamagata lineage viruses,B/Sichuan-Gaoxin/1110/2012,was confirmed to be an intra4ineage reassortant with NA gene from B Victoria lineage.Conclusion The activity of B Victoria lineage virus was stronger than Yamagata lineage virus in the mainland of China during 2012-2013 influenza season,but only Yamagata lineage virus was included in the WHO recommended trivalent influenza vaccine for this period,which could not provide protection to B Victoria lineage virus infection.