title: Studies with inactivated equine influenza vaccine. 1. Serological responses of ponies to graded doses of vaccine.
abstract: Serological responses to three bivalent aqueous equine influenza vaccines of different potency and an adjuvanted bivalent vaccine containing inactivated A/equine/Prague/56 (H7N7) and A/equine/Miami/63 (H3N8) viruses, were examined in seronegative ponies. Potencies of the vaccines, measured by single-radial-diffusion tests, ranged from 4 to 56 micrograms of haemagglutinin (HA) antigen activity/virus strain per dose. Serological responses to vaccination were examined by haemagglutination-inhibition (HI) and single-radial-haemolysis (SRH) tests. Four weeks after a primary dose, HI responses to both vaccine viruses were barely detectable; after a second dose the HI responses to A/Miami/63 virus were low or undetectable but HI responses to A/Prague/56 virus were higher (17/20 ponies with titres greater than or equal to 1:16). In contrast SRH tests revealed dose-related antibody responses to both virus strains after one and two vaccine doses; levels after the second dose were 2- to 5-fold higher than after the primary dose. Highest post-vaccination antibody titres were obtained with the adjuvanted vaccine which contained 2- to 4-fold less antigen (13-23 micrograms HA) than the most potent aqueous vaccine. Post-vaccination antibody reacted well in SRH tests with recent antigenic variants of equine influenza virus. A remarkable finding was the high rate of decline in antibody, detected by HI or SRH tests, following one or two doses of vaccine. Even in animals with the highest post-vaccine antibody levels 2-4 weeks after a booster dose, antibody levels had declined to low or indetectable levels 14 weeks later. The low antibody titres detected at 14-32 weeks after vaccination were nevertheless vaccine dose-related.
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000032:analysis*; D004306:Dose-Response Relationship, Immunologic; D006385:Hemagglutination Inhibition Tests; D006462:Hemolytic Plaque Technique; D006736:Horses / Q000276:immunology*; D007117:Immunization, Secondary; D009980:Influenza A virus / Q000276:immunology*; D013997:Time Factors; D014611:Vaccination / Q000662:veterinary*; D014765:Viral Vaccines / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral; D014765:Viral Vaccines