In a head-to-head comparison, a quadrivalent recombinant influenza vaccine (RIV4) provided more protection in adults aged 50 years or older than a standard-dose, egg-grown, quadrivalent, inactivated influenza vaccine (IIV4). The vaccines were evaluated during the 2014-2015 influenza season, when an antigenic mismatch between circulating and vaccine influenza strains resulted in low vaccine efficacy, according to a New England Journal of Medicinestudy.