Age distribution of influenza like illness cases during post-pandemic A(H3N2): comparison with the twelve previous seasons, in France

PLoS One. 2013 Jun 5;8(6):e65919. doi: 10.1371/journal.pone.0065919. Print 2013.

Abstract

In France, the 2011-2012 influenza epidemic was characterized by the circulation of antigenically drifted influenza A(H3N2) viruses and by an increased disease severity and mortality among the elderly, with respect to the A(H1N1)pdm09 pandemic and post-pandemic outbreaks. Whether the epidemiology of influenza in France differed between the 2011-2012 epidemic and the previous outbreaks is unclear. Here, we analyse the age distribution of influenza like illness (ILI) cases attended in general practice during the 2011-2012 epidemic, and compare it with that of the twelve previous epidemic seasons. Influenza like illness data were obtained through a nationwide surveillance system based on sentinel general practitioners. Vaccine effectiveness was also estimated. The estimated number of ILI cases attended in general practice during the 2011-2012 was lower than that of the past twelve epidemics. The age distribution was characteristic of previous A(H3N2)-dominated outbreaks: school-age children were relatively spared compared to epidemics (co-)dominated by A(H1N1) and/or B viruses (including the 2009 pandemic and post-pandemic outbreaks), while the proportion of adults over 30 year-old was higher. The estimated vaccine effectiveness (54%, 95% CI (48, 60)) was in the lower range for A(H3N2) epidemics. In conclusion, the age distribution of ILI cases attended in general practice seems to be not different between the A(H3N2) pre-pandemic and post-pandemic epidemics. Future researches including a more important number of ILI epidemics and confirmed virological data of influenza and other respiratory pathogens are necessary to confirm these results.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adolescent
  • Adult
  • Age Distribution
  • Aged
  • Child
  • Child, Preschool
  • France / epidemiology
  • Humans
  • Incidence
  • Infant
  • Influenza A Virus, H3N2 Subtype / immunology*
  • Influenza, Human / epidemiology*
  • Influenza, Human / prevention & control
  • Middle Aged
  • Pandemics*
  • Seasons
  • Vaccination
  • Young Adult

Grants and funding

The study was funded by National Institute for Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.