Efficacy of dual vaccination of pandemic H1N1 2009 influenza and seasonal influenza on institutionalized elderly: A one-year prospective cohort study

► Dual vaccination of seasonal influenza and H1N1 2009 in institutionalized elderly. ► Functional status and comorbidity assessed to minimize healthy vaccine bias. ► Dual vaccination was better than vaccination of seasonal influenza alone. ► Reduce all cause mortality and hospitalization by dual vaccination.