title: Circulation of influenza B lineages in northern Viet Nam, 2007-2014.
abstract: BACKGROUND
  Influenza B viruses circulate throughout Viet Nam, and their activities vary by region. There have been two antigenically distinct lineages of influenza B viruses co-circulating in the past 20 years; however, only one lineage is selected as a component of contemporary trivalent seasonal influenza vaccines. To improve the understanding of circulating influenza B lineages and influenza vaccine mismatches, we report the virus lineages circulating in northern Viet Nam over an eight-year period (2007-2014).
  
  
  METHODS
  Lineages of 331 influenza B viruses were characterized by haemagglutination inhibition assay against standard reference ferret (Yamagata) and sheep (Victoria) antisera. Sequence analysis of the haemagglutinin gene was performed in 64 selected influenza B isolates.
  
  
  RESULTS
  The proportion of influenza B lineages changed by year. The Yamagata lineage predominated in 2007, 2008 and 2012; the Victoria lineage predominated in 2009-2014 except 2012. The two lineages showed continuous evolution over time. The Northern Hemisphere's influenza vaccine components were mismatched with the predominant circulating viruses in 2007, 2009 and 2014.
  
  
  CONCLUSIONS
  The seasonality of influenza B activity is more variable in tropical and subtropical regions than in temperate zones. Our data showed a common co-circulation of both influenza B lineages in northern Viet Nam, and it was difficult to predict which one was the predominant lineage. Quadrivalent influenza vaccines containing both lineages may improve the effectiveness of influenza vaccine programmes in the future.
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Thi Thanh
authors.initials: TT
authors.lastname: Le
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Thu Hang
authors.initials: TH
authors.lastname: Pham
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Thi Hien
authors.initials: TH
authors.lastname: Pham
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Le Khanh Hang
authors.initials: le KH
authors.lastname: Nguyen
authors.forename: Co Thach
authors.initials: CT
authors.lastname: Nguyen
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Vu Mai Phuong
authors.initials: VM
authors.lastname: Hoang
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Thu Huong
authors.initials: TH
authors.lastname: Tran
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Vu Son
authors.initials: VS
authors.lastname: Nguyen
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Huong Giang
authors.initials: HG
authors.lastname: Ngo
authors.affiliation: National Institute of Hygiene and Epidemiology, Ha Noi, Viet Nam .
authors.forename: Quynh Mai
authors.initials: QM
authors.lastname: Le
mesh_terms: D000956:Antigens, Viral / Q000032:analysis; D005260:Female; D006385:Hemagglutination Inhibition Tests; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D006801:Humans; D009981:Influenza B virus / Q000145:classification / Q000235:genetics / Q000276:immunology; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control / Q000821:virology*; D008297:Male; D010802:Phylogeny; D018571:Sentinel Surveillance; D017422:Sequence Analysis, DNA; D014744:Vietnam / Q000453:epidemiology
chemical_list: D000956:Antigens, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines