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.
BACKGROUND
Swine influenza A virus (IAV) reassortment with 2009 H1N1 pandemic (H1N1pdm09) virus has been documented, and new genotypes and subclusters of H3N2 have since expanded in the US 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 a vaccine derived from whole inactivated virus (WIV) was compared with live attenuated influenza virus (LAIV) against H3N2.


RESULTS
Hemagglutinin inhibition 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 United States 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.
Virus and Prion Research Unit, National Animal Disease Center, USDA-ARS, Ames, IA, USA.
Pravina
P
Kitikoon
Phillip C
PC
Gauger
Tavis K
TK
Anderson
Marie R
MR
Culhane
Sabrina
S
Swenson
Crystal L
CL
Loving
Daniel R
DR
Perez
Amy L
AL
Vincent
D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology; D003429:Cross Reactions; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D009976:Orthomyxoviridae Infections / Q000276:immunology / Q000517:prevention & control / Q000662:veterinary* / Q000821:virology; D013552:Swine; D013553:Swine Diseases / Q000276:immunology* / Q000517:prevention & control / Q000821:virology; D014481:United States
D000914:Antibodies, Viral; D007252:Influenza Vaccines
Antigenic drift; H3N2v; hemagglutinin inhibition; influenza A virus; maternally derived antibody; vaccines