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.

The Vaccination and Travel Medicine Center University Hospital 500 03 Hradec Kralove Czech Republic

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Hemagglutination Inhibition Antibody Titers as a Correlate of Protection Against Seasonal A/H3N2 Influenza Disease

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ClinicalTrials.gov
NCT00363870