Vaccine-mediated protection of pigs against infection with pandemic H1N1 2009 swine influenza A virus requires a close antigenic match between the vaccine antigen and challenge virus

Abstract Swine influenzaA virus(SwIV) infection has considerable economic and animal welfareconsequences and, because of the zoonotic potential, can also have public health implications. The 2009 pandemicH1N1 ‘swine-origin’ infection is now endemic in both pigs and humans. In Europe, avian-like H1 av N1, human-like H1 hu N2, human-like swine H3N2 and, since 2009, pandemicH1N1 (pH1N1) lineage viruses and reassortants, constitute the dominant subtypes. In this study, we used a swine pH1N1 challenge virus to investigate the efficacy of whole inactivated virus vaccines homologous or heterologous to the challenge virus as well as a commercial vaccine. We found that vaccine-mediated protection was most effective when vaccine antigen and challenge virus were homologous and correlated with the specific production of neutralising antibodiesand a cellular response to the challenge virus. We conclude that a conventional whole inactivated SwIV vaccine must be antigenically matched to the challenge strain to be an effective control measure.