Location: Virus and Prion ResearchTitle: Efficacy of inactivated and live-attenuated influenza virus vaccines in pigs against infection and transmission of emerging H3N2 similar to the 2011-2012 H3N2v Author
|Kehrli Jr, Marcus|
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2013
Publication Date: 9/1/2013
Citation: Loving, C.L., Lager, K.M., Vincent, A.L., Brockmeier, S.L., Gauger, P.C., Anderson, T.K., Kitikoon, P., Perez, D.R., Kehrli, Jr., M.E. 2013. Efficacy in pigs of inactivated and live attenuated influenza virus vaccines against infection and transmission of an emerging H3N2 similar to the 2011-2012 H3N2v. Journal of Virology. 87(17):9895-903. Interpretive Summary: Influenza virus spillover from pigs to people is concern for both public health officials as well as swine producers. In 2012 there were more than 300 cases reported in which a particular strain of swine influenza virus was isolated from people, the majority occurring at agricultural fairs in the summer. One method to limit transmission of the virus from pigs to people is to control the virus in pigs through vaccination. The objective of this study was to evaluate currently available commercial swine influenza vaccines and experimental vaccines at limiting replication and spread of a strain of swine influenza associated with spillover at agricultural fairs in 2012. One commercial vaccine provided significant protection, but it did not prevent transmission of the virus to non-vaccinated pigs in a neighboring pen. One experimental vaccine that is a live-attenuated virus given to pigs in the nose was able to prevent infection. A standard test that uses blood from vaccinated pigs to predict if a pig would be protected from infection was not accurate for commercial or experimental vaccines. The results from this work will provide pig owners and agricultural personnel experimental data for determining the value of commercial vaccines at limiting infection with this particular strain of swine influenza virus, which should contribute to decreasing the frequency of spillover from pigs to people. It also highlights the need for future work to develop assays that are predictive of a vaccines effectiveness.
Technical Abstract: Vaccines provide a primary means to limit disease but may not be effective at blocking infection and pathogen transmission. The objective of the current study was to evaluate the efficacy of commercial inactivated swine influenza A virus (IAV) vaccines and experimental live-attenuated influenza virus (LAIV) vaccines against infection with H3N2 virus and subsequent indirect transmission to naïve pigs. The H3N2 virus evaluated was similar to the H3N2v detected in humans during 2011-12, which was associated with swine contact at agricultural fairs. One commercial vaccine provided partial protection measured by reduced nasal shedding, however, indirect contacts became infected, indicating the reduction in nasal shedding did not prevent aerosol transmission. One LAIV vaccine provided complete protection and none of the indirect contact pigs became infected. Clinical disease was not observed in any group including non-vaccinated animals, a consistent observation in pigs infected with contemporary reassortant H3N2 swine viruses. Serum hemagglutination inhibition titers against the challenge virus were not predictive of efficacy: titers following vaccination with a LAIV that provided sterilizing immunity were below the level considered protective; yet titers in a commercial vaccine group that was not protected were above this same level. While vaccination with currently approved commercial inactivated products did not fully prevent transmission, certain vaccines may provide benefit for limiting shedding, transmission and zoonotic spillover of antigenically similar H3N2 viruses at agriculture fairs when administered appropriately and used in conjunction with additional control measures.