Efficacy of inactivated split-virus influenza vaccine against culture-confirmed influenza in healthy adults: a prospective, randomized, placebo-controlled trial

J Infect Dis. 2009 Dec 15;200(12):1861-9. doi: 10.1086/648406.


Background: A new trivalent inactivated split-virus influenza vaccine (TIV) was recently introduced in the United States. We assessed the efficacy of TIV against culture-confirmed influenza A and/or B.

Methods: In this double-blind trial conducted from September 2006 to May 2007 in the Czech Republic and Finland, participants aged 18-64 years were randomized to receive 1 dose of TIV (n = 5103) or placebo (n = 2549). Influenza-like illnesses (ILI) (defined as at least 1 systemic symptom [fever {oral temperature, > or = 37.8 degrees C} and/or myalgia] and at least 1 respiratory symptom [cough and/or sore throat]) were identified by both active (biweekly phone contact) and passive surveillance. Nasal and throat swab specimens were collected for viral culture.

Results: The attack rate for culture-confirmed ILI was 3.2% in the placebo group, with most strains identified as influenza A (all except 1 were H3N2) matching the vaccine strain. There were 6 cases of influenza B, all of which were of a different lineage (Yamagata) than the vaccine strain. Vaccine efficacy against culture-confirmed influenza A and/or B due to strains antigenically matched to the vaccine was 66.9% (95% confidence interval [CI], 51.9%-77.4%; P < .001) and to any strain was 61.6% (95% CI, 46.0%-72.8%; P < .001).

Conclusion: TIV is efficacious against culture-confirmed influenza in healthy adults.

Trial registration: ClinicalTrials.gov identifier: NCT00363870.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Czech Republic
  • Double-Blind Method
  • Female
  • Finland
  • Humans
  • Influenza A Virus, H1N1 Subtype / immunology
  • Influenza A Virus, H1N1 Subtype / isolation & purification
  • Influenza A Virus, H3N2 Subtype / immunology
  • Influenza A Virus, H3N2 Subtype / isolation & purification
  • Influenza B virus / immunology
  • Influenza B virus / isolation & purification
  • Influenza Vaccines / immunology*
  • Influenza, Human / prevention & control*
  • Influenza, Human / virology
  • Male
  • Middle Aged
  • Placebos / administration & dosage
  • Prospective Studies
  • Vaccines, Inactivated / immunology
  • Vaccines, Subunit / immunology
  • Young Adult


  • Influenza Vaccines
  • Placebos
  • Vaccines, Inactivated
  • Vaccines, Subunit

Associated data

  • ClinicalTrials.gov/NCT00363870