An Equine Influenza Vaccine Containing a Recent Epidemic Strain

Abstract

The equine influenza vaccine in Japan, has been used since 1985. The vaccine contains inactivated virus strains, A/equine/Newmarket/1/77 (H7N7), A/equine/Tokyo/2/71 (H3N8) and A/equine/Kentucky/1/81 (H3N8). Viruses which have currently spread worldwide are predominantly H3N8 viruses. Influenza epidemics involving vaccinated horses have occurred in Europe and the United States after 1989. Some of the current field isolates are antigenically and genetically distinct from the vaccine strains. Therefore, four field isolates were analyzed for their antigenicity and immunogenicity. Among those, A/equine/La Plata/93 (H3N8) showed ideal properties as a new vaccine strain, and A/equine/Kentucky/1/81 was still immunogenic against some of the field isolates. A/equine/Newmarket/1/77, A/equine/Kentucky/1/81 and A/equine/La Plata/93 were, therefore, contained in the test vaccine. The test vaccine (containing these 2 strains) induced sufficient immune response to current field isolates in horses. The new vaccine has been marketed since September of 1996.