Antigenic Relationships between Epidemic Strains and Vaccine Strains of Equine H3 lnfluenza Viruses

Abstract

To confirm whether influenza A/equine-2: H3N8 viruses contained in vaccines presently available in Japan correspond to recent epidemic A/equine-2 viruses, the antigenic relationship between 12 epidemic strains (isolated in six countries from 1979 to 1993) and two A/equine-2 vaccine strains (A/equine/Tokyo/2/71 and equine/Kentucky/1/81) was studied by using guinea pig antisera against the vaccine strains and the serum from a vaccinated horse. Ten epidemic strains possessed close antigenicity to A/equine/Kentucky/1/81, but two strains (and possibly a third) isolated in England in 1979 and 1991 showed different antigenicity to A/equine/Kentucky/1/81. On the other hand, the antigenicity of all 12 epidemic strains was different from that of A/equine/Tokyo/2/71. These results suggest that strains which correspond to recent epidemic strains should be used as vaccine strains in order to ensure a higher level of Prevention.