The efficacy of influenza vaccination in elderly individuals. A randomized double-blind placebo-controlled trial.
OBJECTIVE
To determine the efficacy of influenza vaccination in elderly people.


METHODS
Randomized double-blind placebo-controlled trial.


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


METHODS
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.


METHODS
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).


METHODS
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.


CONCLUSIONS
In the elderly, influenza vaccination may halve the incidence of serological and clinical influenza (in periods of antigenic drift).
Department of General Practice, University of Limburg, Maastricht, The Netherlands.
T M
TM
Govaert
C T
CT
Thijs
N
N
Masurel
M J
MJ
Sprenger
G J
GJ
Dinant
J A
JA
Knottnerus
D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000096:biosynthesis; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D009980:Influenza A virus / Q000276:immunology; D009981:Influenza B virus / Q000276:immunology; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000175:diagnosis / Q000517:prevention & control*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012306:Risk; D011795:Surveys and Questionnaires
D000914:Antibodies, Viral; D007252:Influenza Vaccines