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December 7, 1994

The Efficacy of Influenza Vaccination in Elderly Individuals: A Randomized Double-blind Placebo-Controlled Trial

Author Affiliations

From the Departments of General Practice (Drs Govaert, Dinant, and Knottnerus) and Epidemiology (Dr Thijs), University of Limburg, Maastricht, the Netherlands; Department of Virology and WHO Influenza Centre, Erasmus University, Rotterdam, the Netherlands (Drs Masurel and Sprenger); and Department of Infectious Diseases Epidemiology, National Institute of Public Health and Environmental Protection, Bilthoven, the Netherlands (Dr Sprenger).

JAMA. 1994;272(21):1661-1665. doi:10.1001/jama.1994.03520210045030

Objective.  —To determine the efficacy of influenza vaccination in elderly people.

Design.  —Randomized double-blind placebo-controlled trial.

Setting.  —Fifteen family practices in the Netherlands during influenza season 1991-1992.

Participants.  —A total of 1838 subjects aged 60 years or older, not known as belonging to those high-risk groups in which vaccination was previously given.

Intervention.  —Purified split-virion vaccine containing A/Singapore/6/86(H1N1), A/Beijing/353/89(H3N2), B/Beijing/1/87, and B/Panama/45/90 (n=927) or intramuscular placebo containing physiological saline solution (n=911).

Main Outcome Measures.  —Patients presenting with influenzalike illness up to 5 months after vaccination; self-reported influenza in postal questionnaires 10 weeks and 5 months after vaccination; serological influenza (fourfold increase of antibody titer between 3 weeks and 5 months after vaccination).

Results.  —The incidence of serological influenza was 4% in the vaccine group and 9% in the placebo group (relative risk [RR], 0.50; 95% confidence interval [CI], 0.35 to 0.61). The incidences of clinical influenza were 2% and 3%, respectively (RR, 0.53; 95% CI, 0.39 to 0.73). The effect was strongest for the combination of serological and clinical influenza (RR, 0.42; 95% CI, 0.23 to 0.74). The effect was less pronounced for self-reported influenza.

Conclusion.  —In the elderly, influenza vaccination may halve the incidence of serological and clinical influenza (in periods of antigenic drift).(JAMA. 1994;272:1661-1665)

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