title: Virological characterization of influenza H1N1pdm09 in Vietnam, 2010-2013.
abstract: OBJECTIVE
  Influenza A/H1N1pdm09 virus was first detected in Vietnam on May 31, 2009, and continues to circulate in Vietnam as a seasonal influenza virus. This study has monitored genotypic and phenotypic changes in this group of viruses during 2010-2013 period.
  
  
  METHODS
  We sequenced hemagglutinin (HA) and neuraminidase (NA) genes from representative influenza A/H1N1pdm09 and compared with vaccine strain A/California/07/09 and other contemporary isolates from neighboring countries. Hemagglutination inhibition (HI) and neuraminidase inhibition (NAI) assays also were performed on these isolates.
  
  
  METHODS
  Representative influenza A/H1N1pdm09 isolates (n = 61) from ILI and SARI surveillances in northern Vietnam between 2010 and 2013.
  
  
  RESULTS
  The HA and NA phylogenies revealed six and seven groups, respectively. Five isolates (8·2%) had substitutions G155E and N156K in the HA, which were associated with reduced HI titers by antiserum raised against the vaccine virus A/California/07/2009. One isolate from 2011 and one isolate from 2013 had a predicted H275Y substitution in the neuraminidase molecule, which was associated with reduced susceptibility to oseltamivir in a NAI assay. We also identified a D222N change in the HA of a virus isolated from a fatal case in 2013.
  
  
  CONCLUSIONS
  Significant genotypic and phenotypic changes in A/ H1N1pdm09 influenza viruses were detected by the National Influenza Surveillance System (NISS) in Vietnam between 2010 and 2013 highlighting the value of this system to Vietnam and to the region. Sustained NISS and continued virological monitoring of seasonal influenza viruses are required for vaccine policy development in Vietnam. 3.
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Hang K L
authors.initials: HK
authors.lastname: Nguyen
authors.affiliation: 108 Military Central Hospital, Hanoi, Vietnam.
authors.forename: Phuong T K
authors.initials: PT
authors.lastname: Nguyen
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Thach C
authors.initials: TC
authors.lastname: Nguyen
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Phuong V M
authors.initials: PV
authors.lastname: Hoang
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Thanh T
authors.initials: TT
authors.lastname: Le
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Cuong D
authors.initials: CD
authors.lastname: Vuong
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Anh P
authors.initials: AP
authors.lastname: Nguyen
authors.affiliation: National Hospital of Traditional Medicine, Hanoi, Vietnam.
authors.forename: Loan T T
authors.initials: LT
authors.lastname: Tran
authors.affiliation: Bach Mai Hospital, Hanoi, Vietnam.
authors.forename: Binh G
authors.initials: BG
authors.lastname: Nguyen
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Mai Q
authors.initials: MQ
authors.lastname: Lê
mesh_terms: D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology / Q000821:virology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D014744:Vietnam / Q000453:epidemiology; D014764:Viral Proteins / Q000235:genetics
chemical_list: D014764:Viral Proteins
keywords: Influenza A/H1N1pdm09; Vietnam; the vaccine virus A/California/07/2009; virological characterization