Influenza-like Illness Incidence Is Not Reduced by Influenza Vaccination in a Cohort of Older Adults, Despite Effectively Reducing Laboratory-Confirmed Influenza Virus Infections

J Infect Dis. 2017 Aug 15;216(4):415-424. doi: 10.1093/infdis/jix268.


Background: Data on the relative contribution of influenza virus and other respiratory pathogens to respiratory infections in community-dwelling older adults (≥60 years) are needed.

Methods: A prospective observational cohort study was performed in the Netherlands during 2 winters. Nasopharyngeal and oropharyngeal swabs were collected during influenza-like illness (ILI) episodes and from controls. Viruses and bacteria were identified by multiplex ligation-dependent probe amplification assay and conventional bacterial culture.

Results: The ILI incidence in the consecutive seasons was 7.2% and 11.6%, and influenza virus caused 18.9% and 34.2% of ILI episodes. Potential pathogen were detected in 80% of the ILI events with influenza virus, coronaviruses, rhinoviruses, human metapneumovirus, respiratory syncytial virus, parainfluenza viruses, and Haemophilus influenzae being the most common. Influenza vaccination reduced influenza virus infection by 73% (95% confidence interval [CI], 26%-90%) and 51% (95% CI, 7%-74%) in ILI patients. However, ILI incidence was similar between vaccinated (7.6% and 10.8%) and nonvaccinated (4.2% and 11.4%) participants in 2011-2012 and 2012-2013, respectively (P > .05).

Conclusions: Influenza virus is a frequent pathogen in older adults with ILI. Vaccination reduces the number of influenza virus infections but not the overall number of ILI episodes: other pathogens fill the gap. We suggest the existence of a pool of individuals with high susceptibility to respiratory infections.

Clinical trials registration: NTR3386.

Keywords: influenza virus; influenza virus infection; influenza-like illness; older adults; vaccination.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Female
  • Follow-Up Studies
  • Humans
  • Incidence
  • Independent Living
  • Influenza Vaccines / administration & dosage
  • Influenza Vaccines / therapeutic use*
  • Influenza, Human / epidemiology*
  • Influenza, Human / prevention & control
  • Male
  • Middle Aged
  • Multiplex Polymerase Chain Reaction
  • Nasopharynx / virology
  • Netherlands / epidemiology
  • Prospective Studies
  • Respiratory Tract Infections / epidemiology*
  • Respiratory Tract Infections / prevention & control
  • Seasons
  • Vaccination*


  • Influenza Vaccines