Influenza vaccine in over-65s |
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Systematic review
In that wonderful city of Melbourne, the authors used an extensive search strategy for studies in any language where inactivated influenza vaccine was used, the study period was determined by influenza surveillance, and the population was community-based elders of 65 years or more. Excluded were studies on institutionalised persons, where comparability of study groups was not reported, studies with a cross-sectional design and those where influenza strains used did not match circulating strains, or where this was not reported.
The outcome used was vaccine effectiveness. Vaccine effectiveness (VE) is given by the equation:
VE = (1 - relative risk) x 100
Thus a relative risk of 0.5 in an outcome gives a vaccine effectiveness of 50%, or a 50% reduction in the rate of that outcome over control.
Results
There were 15 studies. One was a randomised trial ( Bandolier 11 ), two others were labelled as clinical trials, and the remainder were case-control or cohort studies. Results of vaccine effectiveness for different outcomes are shown in Figure 1. The biggest effect was on mortality.
Figure 1: Vaccine effectiveness of influenza vaccine in the over 65s measured by different outcomes
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