Antibody Responses against American and European Lineage Strains of Equine-2 Influenza Virus among Racehorses Inoculated with the New Vaccine

Abstract

A new equine influenza vaccine, which contains A/equine/La Plata/93 (American lineage virus) and A/equine/Avesta/93 (European lineage virus), became commercially available in 2004. To investigate the antibody responses of racehorses inoculated with the new vaccine, hemagglutination inhibition (HI) antibody titer levels against A/equine/La Plata/93 and A/equine/Avesta/93 were measured using sera samples collected from racehorses at the Ritto Training Center from 2004 to 2005. Three-year-old and four-year-old horses inoculated with the new vaccine once or twice as booster immunization possessed comparatively high level HI antibody titers against A/equine/La Plata/93, however, they possessed low level HI antibody titers against A/equine/Avesta/93. Two-year-old horses inoculated with the new vaccine from the beginning of their vaccination history possessed comparatively high levels of HI antibody titers against both strains.