Location: Virus and Prion ResearchTitle: Swine influenza virus vaccine serologic cross-reactivity to contemporary U.S. swine H3N2 and efficacy in pigs infected with an H3N2 similar to 2011-2012 H3N2v Author
Submitted to: Influenza and Other Respiratory Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2013
Publication Date: 12/1/2013
Citation: Kitikoon, P., Gauger, P.C., Anderson, T.K., Culhane, M.R., Swenson, S., Loving, C.L., Perez, D.R., Vincent, A.L. 2013. Swine influenza virus vaccine serologic cross-reactivity to contemporary US swine H3N2 and efficacy in pigs infected with an H3N2 similar to 2011-2012 H3N2v. Influenza and Other Respiratory Viruses. 7(Suppl. 4):32-41. Interpretive Summary: Swine influenza continues to be a major problem for swine producers. The introduction and reassortment of the 2009 H1N1 pandemic virus with endemic U.S. swine H3N2 viruses increased antigenic diversity and generated a new reassortant strain that caused a public health concern. This study indicates that contemporary swine H3N2 viruses are drifting from the currently available vaccines. A vaccine-challenge trial was conducted to evaluate commercial vaccine efficacy and compare different platform vaccines against a reassorted swine H3N2 (rH3N2p) virus infection in pigs. The rH3N2p virus is similar to H3N2 variant viruses isolated from infected people in 2011-2012 and generated mild disease in pigs but replicates and sheds well from the nasal cavities. Commercial inactivated vaccine reduced virus in lungs and nasal cavities in pigs with no maternally derived antibodies (MDA) but the presence of MDA at vaccination impaired the vaccine efficacy with indication of causing enhanced disease. The finding suggests that extensive use of inactivated vaccines in sows to increase MDA that is likely to mismatched to the circulating strains to which piglets are exposed should be re-evaluated. In addition this study indicated that inactivated vaccine reduced shedding while live attenuated vaccine with identical vaccine strain limited virus shedding in infected pigs. Vaccination remains an important tool in controlling influenza virus in pig production systems and can help limit transmission of virus to people. The antigenic diversity of virus in swine makes development of adequate inactivated vaccines challenging. Our vaccine study underscore the need for improving the process of swine influenza vaccine strain updates as well as consideration to the use of other appropriate vaccine platforms.
Technical Abstract: Background: Swine influenza A virus (IAV) reassortment with 2009 H1N1 pandemic (H1N1pdm09) virus has been documented and new genotypes and sub-clusters of H3N2 have since expanded in the U.S. swine population. An H3N2 variant (H3N2v) virus with the H1N1pdm09 matrix gene and the remaining genes of swine triple reassortant H3N2 caused outbreaks at agricultural fairs in 2011-2012. Methods: To assess commercial swine IAV vaccines’ efficacy against H3N2 viruses, including those similar to H3N2v, antisera to three vaccines were tested by hemagglutinin-inhibition (HI) assay against contemporary H3N2. Vaccine 1, with high HI cross-reactivity, was further investigated for efficacy against H3N2 virus infection in pigs with or without maternally derived antibodies (MDA). In addition, efficacy of vaccines derived from whole inactivated virus (WIV) was compared to live attenuated influenza virus (LAIV) against H3N2. Results: HI cross-reactivity demonstrated that contemporary swine H3N2 viruses have drifted from viruses in current swine IAV vaccines. The vaccine with the highest level of HI cross-reactivity significantly protected pigs without MDA. However, the presence of MDA at vaccination blocked vaccine efficacy. The performance of WIV and LAIV was comparable in the absence of MDA. Conclusions: Swine IAV in the U.S. is complex and dynamic. Vaccination to minimize virus shedding can help limit transmission of virus among pigs and people. However, vaccines must be updated. A critical review of the use of WIV in sows is required in the context of the current IAV ecology and vaccine application in pigs with MDA.