After the 2009 pandemic, variant H3N2 swine influenza viruses (H3N2v SIV) carrying genes from pandemic H1N1 emerged in pig farms. The objective of this study is to investigate whether the two live vaccine candidates developed in our lab would provide protection to newly emerging H3N2 SIV infection and control virus transmission in pigs.

Two pig trials were conducted for the purpose of the study. First was to evaluate the pathogenicity and transmissibility of H3N2v SIV. A group of pigs (principal infection group) were infected with H3N2v SIV. Then, we introduced a group of healthy pigs (contact group) into the same pen to investigate the direct contact transmission. Contact group stayed with principal infection group for 3 days. The principal pigs infected with H3N2 SIV started to shed large amount of virus in nasal mucus at 24 hours after the infection. The contact pigs also started to shed virus in their nasal mucus at 24 hours after contact with principal group. H3N2v virus infection did not cause fever and other SIV symptoms such as coughing, anorexia, depression but induced lung lesion, which was observed in both principal infection and contact groups. After assessment of pathogenicity and transmissibility of H3N2v SIV, we conducted a similar transmission study in pigs but this time the principal pigs were vaccinated twice with various SIV vaccines; FluSure XP or live SIV vaccines before the H3N2v virus infection. The contact pigs were introduced into the pen of each principal group after the virus infection. All vaccine groups developed antibody response to H3N2v virus but only FluSure XP vaccine group induced protective antibodies. Vaccination of FluSure XP reduced number of pigs shedding virus as well as the amount of shed virus. However, this delayed virus transmission resulted delayed viral clearance in its contact group. Although FluSure XP and live SIV vaccines provided partial protection against A/swine/Kansas/11-110529/2011 (H3N2v) infection since no virus was detected in lung tissues in vaccine groups, both commercial and live vaccines failed to effectively control the transmission of H3N2v virus to healthy contact pigs. Of note that herd vaccination of FluSure XP may control the H3N2v transmission at some level since all the pigs in the herd developed immune responses against H3N2v. In conclusion, inability of vaccines to control the transmission of emerging variant viruses emphasizes the importance of continuous surveillance of SIV circulating in swine farm and vaccine updates.

Contact information: Yan Zhou, Ph.D.
Vaccine and Infectious Disease Organization-International Vaccine Centre (VIDO-InterVac), University of Saskatchewan 120 Veterinary Road, Saskatoon, SK, Canada, S7N 5E3
Phone: 306-966-7716""; Fax: 306-966-7478"" ; Email: [email protected]