It has been estimated that annual seasonal influenza epidemics result in three to five million cases of severe illness and up to 500.000 deaths worldwide. More than 90% of influenza-related deaths occur in elderly individuals. It has been well documented that the immune response of the elderly to influenza vaccination in terms of the production of antibodies is below that of younger adults and the clinical efficacy of influenza vaccination for the elderly has been recently questioned by several studies. It has been suggested that providing vaccination against influenza to schoolchildren may provide indirect protection for older adults, since children are important spreaders of influenza within their communities. However, to our knowledge there has been no systematic review assessing the effectiveness of that strategy to prevent influenza and its complications in older adults. Hence, we propose the present systematic review protocol to assess the evidence of the strategy of vaccinating schoolchildren against influenza as a means to prevent influenza and its complications in older people.Methods: We have already conducted searches in the following databases: MEDLINE, EMBASE, Web of Science, Cochrane Library and LILACS. In addition, we will search the bibliographies of all selected articles for additional references and will contact study author's, experts in the field and pharmaceutical companies for further published and unpublished data. Our search for grey literature will also include the assessment of the following databases: System for information on Grey Literature in Europe, the National Tecnhical Information Service, Clinical Trials.gov, and the World Health Organization International Clinical Trials Registry Platform. The primary outcome of the review is the combined mortality from influenza and/or pneumonia in older adults as assessed by the original investigation. We will assess the quality from clinical trials using the current Cochrane Collaboration's tool for assessing risk of bias. For the assessment of risk of bias of observational studies we will use the Effective Public Health Practice Project Quality Assessment tool. We will analyze the overall strength of the evidence for each outcome using the Grading of Recommendations Assessments, Developments and Evaluation (GRADE) system. For our inferences we will also draw from he concepts of "adequacy, plausibility and probability" for public health interventions developed by Habicht, Victora and Vaughan. Both the process of selection of studies as well as the assessment of risk of bias of individual studies will be conducted by two independent researchers. Any disagreements between the reviewers will be resolved by discussion, with the involvement of a third author as necessary.The protocol of this systematic review was registered in the PROSPERO database (International Prospective Register of Systematic Reviews) under CRD42014003292. We hope that the results of this review will inform future research and public policies against influenza in Brazil and in the World.
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