The Efficacy of Influenza Vaccination in Elderly Individuals

doi:10.1001/jama.1994.03520210045030

The Efficacy of Influenza Vaccination in Elderly Individuals

A Randomized Double-blind Placebo-Controlled Trial

Th. M. E. Govaert, MD, PhD;
C. T. M. C. N. Thijs, MD, PhD;
N. Masurel, MD, PhD;
M. J. W. Sprenger, MD, PhD;
G. J. Dinant, MD, PhD;
J. A. Knottnerus, MD, PhD

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).

Abstract

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)