Efficacy of Inactivated and Live-Attenuated Influenza Virus Vaccines in Pigs against Infection and Transmission of Emerging H3N2 Similar to the 2011-2012 H3N2v

July 10, 2013 — 

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 na�ve 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.

Crystal L. Loving; Kelly M. Lager; Amy L. Vincent; Susan L. Brockmeier; Phillip C. Gauger; Tavis K. Anderson; Pravina Kitikoon; Daniel R. Perez and Marcus E. Kehrli Jr; Efficacy of Inactivated and Live-Attenuated Influenza Virus Vaccines in Pigs against Infection and Transmission of Emerging H3N2 Similar to the 2011-2012 H3N2v; Journal of Virology; Published online July 3, 2013.