Tme. Govaert et al., THE EFFICACY OF INFLUENZA VACCINATION IN ELDERLY INDIVIDUALS - A RANDOMIZED DOUBLE-BLIND PLACEBO-CONTROLLED TRIAL, JAMA, the journal of the American Medical Association, 272(21), 1994, pp. 1661-1665
Objective.-To determine the efficacy of influenza vaccination in elder
ly people. Design.-Randomized double-blind placebo-controlled trial. S
etting.-Fifteen family practices in the Netherlands during influenza s
eason 1991-1992. Participants.-A total of 1838 subjects aged 60 years
or older, not known as belonging to those high-risk groups in which va
ccination was previously given. Intervention.-Purified split-virion va
ccine containing A/Singapore/6/86(H1N1), A/Beijing/353/89(H3N2), B/Bei
jing/l/87, and B/Panama/45/90 (n=927) or intramuscular placebo contain
ing physiological saline solution (n=911). Main Outcome Measures.-Pati
ents presenting with influenzalike illness up to 5 months after vaccin
ation; 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). Resul
ts.-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 we
re 2% and 3%, respectively (RR, 0.53; 95% Cl, 0.39 to 0.73), The effec
t was strongest for the combination of serological and clinical influe
nza (RR, 0.42; 95% Cl, 0.23 to 0.74). The effect was less pronounced f
or self-reported influenza. Conclusion.-In the elderly, influenza vacc
ination may halve the incidence of serological and clinical influenza
(in periods of antigenic drift).