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Arch Intern Med. 1999 Jan 25;159(2):182-8.

Protection against influenza after annually repeated vaccination: a meta-analysis of serologic and field studies.

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  • 1World Health Organization National Influenza Centre, Institute of Virology, Erasmus University, Rotterdam, The Netherlands.

Abstract

BACKGROUND:

According to common recommendations, influenza vaccination should be performed annually. It has been suggested that vaccination in previous years reduces vaccine efficacy in the long term.

OBJECTIVE:

To determine whether the protection of influenza vaccine decreases when vaccination is repeated annually.

METHODS:

Articles published between 1966 and 1997 were selected from MEDLINE. The end point for field studies was the influenza-related morbidity or mortality during influenza outbreaks (resulting in field protection rates). The end point for serologic studies was exceeding a protective postvaccination hemagglutination-inhibition titer (serologic protection rates). Protection rate differences between groups with single and multiple vaccinations were subjected to meta-analysis.

RESULTS:

Seven field studies (including 13 trials) supported the hypothesis that protection in multiple-vaccination groups is at least as good as that in single-vaccination groups. Ten trials with 5117 observations could be subjected to meta-analysis. The pooled protection-rate difference was close to 0 (1.1%; 95% confidence interval, -0.2% to 2.4%), thus detecting no difference between single or multiple vaccination. Twelve serologic studies (including 53 trials) showed heterogeneous results: 9 trials were significantly in favor of single vaccination, and 7 were in favor of multiple vaccination, but in most cases, there was no significant difference between the 2 vaccination groups. The pooled serologic protection-rate difference from 52 trials (12341 observations) was again close to 0 (1.7%; 95% confidence interval, -1.3% to 4.8%).

CONCLUSIONS:

We did not detect any evidence for a decreasing protection with annually repeated influenza vaccination. Annual vaccination should not be discouraged in populations at risk.

PMID:
9927102
[PubMed - indexed for MEDLINE]
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