Fast track — ArticlesEfficacy and effectiveness of influenza vaccines in elderly people: a systematic review
Introduction
Over the past four decades, vaccines have been used to reduce the effects of influenza in elderly individuals. In 2000, 40 of 51 developed or rapidly developing countries recommended vaccination for all individuals aged 60–65 or older,1 and, in 2003, 290 million doses of vaccine were distributed worldwide.2 According to Centres for Disease Control (CDC), the main aim of vaccination in elderly individuals is to reduce the risk of complications in those who are most vulnerable.3, 4 As such, they define two high priority groups—individuals aged 65 years or older, and residents of nursing homes and long-term care facilities.
Two systematic reviews of the effects of influenza vaccines in elderly people have been published.5, 6 The first5 was done more than a decade ago, and the second6 has several methodological weaknesses—namely, the exclusion of studies with denominators of less than 30 and pooling of studies of different design—and includes only 15 studies. Our aim was to identify and assess the comparative studies of the efficacy and effectiveness of influenza vaccines in individuals aged 65 years or older. This review is part of two Cochrane reviews that will also include evidence of safety of the vaccines studied and of their effectiveness in carers.7, 8
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Search strategy
We searched electronic databases to Dec 31, 2004, to identify reports of single studies and systematic reviews published in any language. We searched: the Cochrane Library, including the Cochrane Database of Systematic Reviews, the UK National Health Service (NHS) Database of Abstracts of Reviews of Effectiveness, and the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE (OVID, from January, 1966); EMBASE (Dialog' 1974–79; SilverPlatter from 1980); Biological Abstracts
Results
We included data from 64 studies (96 datasets)16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79 in our analyses (figure 1). Half (n=48) the datasets reported A/H3N2 virus circulating, 4% (n=4) B viruses, 1% (n=1) A/H1N1, 1% (n=1) A/H2N2, and 7% (n=7) reported A/H3N2 and A/H1N1 circulating at
Discussion
Our findings show that, according to reliable evidence, the effectiveness of trivalent inactivated influenza vaccines in elderly individuals is modest, irrespective of setting, outcome, population, and study design.
In view of the known variability of incidence and effect of influenza, we constructed a large number of comparisons and strata to reduce to a minimum possible heterogeneity between studies and to aid comparability. Despite our attempts we noted significant residual between-studies
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