Seasonal influenza vaccine efficacy and its determinants in children and non-elderly adults: A systematic review with meta-analyses of controlled trials

► Summary efficacy was 65% against any strain. ► Live and inactivated vaccines showed similar efficacy for not-matched strains. ► Efficacy against Flu A was higher than against Flu B for not-matched strains. ► Live-attenuated vaccines performed better than inactivated vaccines in children. ► Inactivated vaccines performed better than live-attenuated vaccines in adults.