Elsevier

The Lancet

Volume 366, Issue 9492, 1–7 October 2005, Pages 1165-1174
The Lancet

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Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review

https://doi.org/10.1016/S0140-6736(05)67339-4Get rights and content

Summary

Background

Influenza vaccination of elderly individuals is recommended worldwide. Our aim was to review the evidence of efficacy and effectiveness of influenza vaccines in individuals aged 65 years or older.

Methods

We searched five electronic databases to December, 2004, in any language, for randomised (n=5), cohort (n=49), and case-control (n=10) studies, assessing efficacy against influenza (reduction in laboratory-confirmed cases) or effectiveness against influenza-like illness (reduction in symptomatic cases). We expressed vaccine efficacy or effectiveness as a proportion, using the formula VE=1–relative risk (RR) or VE*=1–odds ratio (OR). We analysed the following outcomes: influenza, influenza-like illness, hospital admissions, complications, and deaths.

Findings

In homes for elderly individuals (with good vaccine match and high viral circulation) the effectiveness of vaccines against influenza-like illness was 23% (95% CI 6–36) and non-significant against influenza (RR 1·04, 0·43–2·51). Well matched vaccines prevented pneumonia (VE 46%, 30–58) and hospital admission (VE 45%, 16–64) for and deaths from influenza or pneumonia (VE 42%, 17–59), and reduced all-cause mortality (VE 60%, 23–79). In elderly individuals living in the community, vaccines were not significantly effective against influenza (RR 0·19, 0·02–2·01), influenza-like illness (RR 1·05, 0·58–1·89), or pneumonia (RR 0·88, 0·64–1·20). Well matched vaccines prevented hospital admission for influenza and pneumonia (VE 26%, 12–38) and all-cause mortality (VE 42%, 24–55). After adjustment for confounders, vaccine performance was improved for admissions to hospital for influenza or pneumonia (VE* 27%, 21–33), respiratory diseases (VE* 22%, 15–28), and cardiac disease (VE* 24%, 18–30), and for all-cause mortality (VE* 47%, 39–54).

Interpretation

In long-term care facilities, where vaccination is most effective against complications, the aims of the vaccination campaign are fulfilled, at least in part. However, according to reliable evidence the usefulness of vaccines in the community is modest.

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

Section snippets

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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