Universal vaccination of children against influenza: Are there indirect benefits to the community?: A systematic review of the evidence
Introduction
Influenza remains a significant cause of morbidity and mortality every year worldwide despite current approaches to prevention and control [1]. Vaccination of groups at high risk of complications (such as the elderly, the chronically ill and young children) is the principal strategy adopted in Europe and North America [2], [3]. However, even with high coverage this can only be partially effective in reducing the impact of influenza because the vaccine is less effective in those chronically ill or frail [4], [5].
A complementary approach to the prevention and control of influenza would be the vaccination of healthy children, who are known to be efficient spreaders of influenza within communities [6]. Vaccinating children might indirectly protect their contacts and potentially lead to a reduction in influenza-related morbidity and mortality in the wider community if the uptake of vaccine was high enough [7].
Although a comprehensive meta-analysis was published in 2005 demonstrating the efficacy of influenza vaccine in healthy children aged >2 years [8], and restimulated the debate around influenza vaccination strategies, a published systematic review of the evidence about the indirect protective effects of the vaccination is still lacking. Appraisal of this literature is essential to inform policy in Europe and elsewhere.
This systematic review assesses the evidence regarding the indirect protective effect of vaccinating children to protect others against influenza.
Section snippets
Search strategy
We searched for primary studies on the effectiveness and cost effectiveness of vaccinating children in order to reduce transmission to others, especially those at high risk, using the following electronic databases up to January 2004: Cochrane Controlled Trials Register; MEDLINE; EMBASE; CINAHL; NHS Economic Evaluation Database (NHS EED); Health Economics Evaluations Database (HEED); and Database of Abstracts of Reviews of Effects (DARE). Combinations of the following search terms were used in
Quantity, quality and characteristics of included studies
The literature search identified over 2500 references, of which 790 potentially relevant titles/abstracts were identified. Eleven studies on effectiveness were finally included [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26] and three economic studies [27], [28], [29]. Fig. 1 indicates the flow of study selection.
Effectiveness studies
The characteristics of the effectiveness studies are given in Table 1a, Table 1b. The included studies varied considerably in design, size, scope,
Key results
Eleven studies have been published which assess the effects on contacts or the wider population of vaccinating children [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]. Overall results are suggestive of indirect protection, but the design problems of these studies mean that this is unproven and the extent of potential benefit difficult to quantify. The best quality randomised study, [14] indicates significant protection against respiratory tract infections in
Acknowledgements
Thanks to Professor Stirling Bryan for his advice on the economic analyses and to Yen-Fu Chen for his research assistance at the beginning of the project. Thank you also to Dr. Richard Pitman (Health Protection Agency) for his advice.
Contributors: MC carried out the systematic review and appraisal of the included studies, co-wrote the underlying report and commented on the text. RJ also undertook the systematic review and appraisal of the included studies and wrote the paper. EA also assisted
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