title: Genetic structure of human A/H1N1 and A/H3N2 influenza virus on Corsica Island: phylogenetic analysis and vaccine strain match, 2006-2010.
abstract: BACKGROUND
  The aim of this study was to analyse the genetic patterns of Hemagglutinin (HA) genes of influenza A strains circulating on Corsica Island during the 2006-2009 epidemic seasons and the 2009-2010 pandemic season.
  
  
  METHODS
  Nasopharyngeal samples from 371 patients with influenza-like illness (ILI) were collected by General Practitioners (GPs) of the Sentinelles Network through a randomised selection routine.
  
  
  RESULTS
  Phylogenetic analysis of HA revealed that A/H3N2 strains circulating on Corsica were closely related to the WHO recommended vaccine strains in each analyzed season (2006-2007 to 2008-2009). Seasonal Corsican influenza A/H1N1 isolated during the 2007-2008 season had drifted towards the A/Brisbane/59/2007 lineage, the A/H1N1 vaccine strain for the 2008-2009 season. The A/H1N1 2009 (A/H1N1pdm) strains isolated on Corsica Island were characterized by the S220T mutation specific to clade 7 isolates. It should be noted that Corsican isolates formed a separate sub-clade of clade 7 as a consequence of the presence of the fixed substitution D222E. The percentages of the perfect match vaccine efficacy, estimated by using the p(epitope) model, against influenza viruses circulating on Corsica Island varied substantially across the four seasons analyzed, and tend to be highest for A/H1N1 compared with A/H3N2 vaccines, suggesting that cross-immunity seems to be stronger for the H1 HA gene.
  
  
  CONCLUSIONS
  The molecular analysis of the HA gene of influenza viruses that circulated on Corsica Island between 2006-2010 showed for each season the presence of a dominant lineage characterized by at least one fixed mutation. The A/H3N2 and A/H1N1pdm isolates were characterized by multiples fixation at antigenic sites. The fixation of specific mutations at each outbreak could be explained by the combination of a neutral phenomenon and a founder effect, favoring the presence of a dominant lineage in a closed environment such as Corsica Island.
authors.affiliation: INSERM, UMR-S 707, F-75012, Paris, France. falchi@u707.jussieu.fr
authors.forename: Alessandra
authors.initials: A
authors.lastname: Falchi
authors.forename: Jean Pierre
authors.initials: JP
authors.lastname: Amoros
authors.forename: Christophe
authors.initials: C
authors.lastname: Arena
authors.forename: Jean
authors.initials: J
authors.lastname: Arrighi
authors.forename: François
authors.initials: F
authors.lastname: Casabianca
authors.forename: Laurent
authors.initials: L
authors.lastname: Andreoletti
authors.forename: Clément
authors.initials: C
authors.lastname: Turbelin
authors.forename: Antoine
authors.initials: A
authors.lastname: Flahault
authors.forename: Thierry
authors.initials: T
authors.lastname: Blanchon
authors.forename: Thomas
authors.initials: T
authors.lastname: Hanslik
authors.forename: Laurent
authors.initials: L
authors.lastname: Varesi
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D005602:France / Q000453:epidemiology; D040342:Genetic Structures / Q000235:genetics; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000235:genetics*; D053122:Influenza A Virus, H3N2 Subtype / Q000145:classification / Q000235:genetics*; D007252:Influenza Vaccines / Q000235:genetics*; D007251:Influenza, Human / Q000453:epidemiology / Q000821:virology; D010802:Phylogeny
chemical_list: D007252:Influenza Vaccines