Influenza vaccine prevents medically attended influenza-associated acute respiratory illness in adults aged ≥50 years

J Infect Dis. 2015 Apr 1;211(7):1045-50. doi: 10.1093/infdis/jiu578. Epub 2014 Oct 21.


Background: There are few estimates of effectiveness influenza vaccine in preventing serious outcomes due to influenza in older adults.

Methods: Adults aged ≥50 years who sought medical care for acute respiratory illness were enrolled. A nose/throat swab was tested for influenza virus by reverse transcription-polymerase chain reaction. Clinical and demographic data were collected, including verification of receipt of trivalent inactivated influenza vaccination (IIV-3). Adjusted odds ratios were estimated by multivariable logistic regression models with an L1 penalty on all covariates except vaccination status.

Results: A total of 1047 subjects were enrolled from November through April during 5 influenza seasons during 2006-2012, excluding the 2009-2010 season. Of those enrolled, 927 (88%) had complete influenza virus testing, vaccination status, and demographic data obtained. Of 86 (9.3%) influenza virus-positive patients, 47 (55%) were vaccinated. Of 841 influenza virus-negative patients, 646 (76.8%) were vaccinated. Over 5 influenza seasons, IIV-3 was 58.4% effective (95% confidence interval [CI], 37.0%-75.6%) for the prevention of medically attended laboratory-confirmed influenza illness in adults aged ≥50 years and 58.4% effective (95% CI, 7.9%-81.1%) in adults aged ≥65 years.

Conclusions: Influenza vaccine was moderately effective in preventing influenza-associated medical care visits in older adults.

Keywords: control-negative; elderly; influenza vaccine effectiveness; older adults.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Case-Control Studies
  • Female
  • Hospitalization
  • Humans
  • Influenza Vaccines / immunology*
  • Influenza, Human / prevention & control*
  • Influenza, Human / virology
  • Logistic Models
  • Male
  • Middle Aged
  • Multivariate Analysis
  • Nose / virology
  • Orthomyxoviridae / immunology*
  • Orthomyxoviridae / isolation & purification
  • Pharynx / virology
  • Prospective Studies
  • Seasons
  • Vaccination*
  • Vaccines, Inactivated


  • Influenza Vaccines
  • Vaccines, Inactivated