title: Genetic characterization of seasonal influenza A (H3N2) viruses in Ontario during 2010-2011 influenza season: high prevalence of mutations at antigenic sites.
abstract: BACKGROUND
  The direct effect of antigenic site mutations in influenza viruses on antigenic drift and vaccine effectiveness is poorly understood.
  
  
  OBJECTIVE
  To investigate the genetic and antigenic characteristics of human influenza A (H3N2) viruses circulating in Ontario during the early 2010-2011 winter season.
  
  
  METHODS
  We sequenced the hemagglutinin (HA) and neuraminidase (NA) genes from 41 A(H3N2) viruses detected in nasopharyngeal specimens. Strain typing was performed by hemagglutination inhibition (HI) assay. Molecular and phylogenetic tree analyses were conducted.
  
  
  RESULTS
  HA and NA genes showed high similarity to the 2010-2011 vaccine strain, A/Perth/16/2009 (H3N2)-like virus (97·7-98·5% and 98·7-99·5% amino acid (AA) identity, respectively). Compared to A/Perth/16/2009 strain, HA gene mutations were documented at 28 different AA positions across all five H3 antigenic sites, with a range of 5-11 mutations in individual viruses. Thirty-six (88%) viruses had 8 AA substitutions in common; none of these had reduced HI titer. Among Ontario isolates, 11 antigenic site AAs were positively selected with an increase in glycosylation sites.
  
  
  CONCLUSIONS
  The presence of antigenic site mutations with high frequency among 2010-2011 influenza H3N2 isolates confirms ongoing adaptive H3N2 evolution. These may represent early phylogenetic changes that could cause antigenic drift with further mutations. Clinical relevance of antigenic site mutations not causing drift in HI assays is unknown and requires further investigation. In addition, viral sequencing information will assist with vaccine strain planning and may facilitate early detection of vaccine escape.
authors: Ontario Agency for Health Protection and Promotion, Toronto, ON, Canada.
authors: Alireza
authors: A
authors: Eshaghi
authors: Venkata R
authors: VR
authors: Duvvuri
authors: Aimin
authors: A
authors: Li
authors: Samir N
authors: SN
authors: Patel
authors: Nathalie
authors: N
authors: Bastien
authors: Yan
authors: Y
authors: Li
authors: Donald E
authors: DE
authors: Low
authors: Jonathan B
authors: JB
authors: Gubbay
mesh_terms: D000956:Antigens, Viral / Q000235:genetics* / Q000276:immunology; D005838:Genotype; D006385:Hemagglutination Inhibition Tests; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics* / Q000276:immunology; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification*; D007251:Influenza, Human / Q000821:virology*; D059645:Mutation Rate; D020125:Mutation, Missense; D009305:Nasopharynx / Q000821:virology; D009439:Neuraminidase / Q000235:genetics* / Q000276:immunology; D009864:Ontario; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics; D017422:Sequence Analysis, DNA; D012703:Serotyping; D014764:Viral Proteins / Q000235:genetics* / Q000276:immunology
chemical_list: D000956:Antigens, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D012367:RNA, Viral; D014764:Viral Proteins; C487630:NA protein, influenza A virus; D009439:Neuraminidase
keywords: Antigenic site mutations; genetic and antigenic characterization; phylogenetic analysis; positive selection analysis; seasonal influenza A (H3N2) virus