Pre- and postpandemic estimates of 2009 pandemic influenza A(H1N1) seroprotection to inform surveillance-based incidence, by age, during the 2013-2014 epidemic in Canada

J Infect Dis. 2015 Jan 1;211(1):109-14. doi: 10.1093/infdis/jiu366. Epub 2014 Jun 27.


To understand the epidemic resurgence of influenza due to the 2009 pandemic influenza A(H1N1) strain (A[H1N1]pdm09) during the 2013-2014 influenza season, we compared age-related cross-sectional estimates of seroprotection before the pandemic (during 2009) and after the pandemic (during 2010 and 2013) to subsequent surveillance-based, laboratory-confirmed incidence of influenza due to A(H1N1)pdm09 in British Columbia, Canada. Prepandemic seroprotection was negligible except for very old adults (defined as adults aged ≥ 80 years), among whom 80% had seroprotection. Conversely, postpandemic seroprotection followed a U-shaped distribution, with detection in approximately 35%-45% of working-aged adults but in ≥ 70% of very old adults and young children, excluding children aged <5 years in 2013, among whom seroprotection again decreased to <20%. The incidence was 5-fold higher during 2013-2014, compared with 2010-2011, and was highest among children aged <5 years and working-aged adults, reflecting a mirror image of the age-based seroprotection data.

Keywords: A(H1N1)pdm09; hemagglutination inhibition; incidence; influenza; seroprotection; serosurvey; surveillance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Viral / immunology
  • British Columbia / epidemiology
  • Child
  • Child, Preschool
  • Cross-Sectional Studies
  • Epidemics*
  • Female
  • Hemagglutination Inhibition Tests / methods
  • Humans
  • Incidence
  • Influenza A Virus, H1N1 Subtype / isolation & purification*
  • Influenza, Human / epidemiology*
  • Male
  • Middle Aged
  • Seasons
  • Young Adult


  • Antibodies, Viral