Effectiveness and Harms of Seasonal and Pandemic Influenza Vaccines in Children Adults and Elderly

The authors completed an umbrella review and reanalyzed data from 15 previously published meta-analyses to determine how different analyses and study selection criteria could explain differences in findings or interpretations. They found statistically significant efficacy and effectiveness – high for laboratory-confirmed cases in children and adults and modest for clinically-confirmed cases and for the elderly – of seasonal influenza vaccines. They identified a scarcity of data on the efficacy of live-attenuated vaccine in those less than two years old, suboptimal quality of harms data, and a lack of meta-analysis on the effect of H1N1 vaccination on clinical outcomes.