Comparative antigenicity and immunogenicity of A/USSR/77 influenza vaccines in normal and primed mice

In response to the threat of wide-spread epidemics of influenza in the United States due to the A/USSR/77 strain of virus, vaccines containing A/USSR/77 virus were prepared by four manufacturers. The vaccines were standardized by immunological measurements of viral hemagglutinin and were tested for their ability to induce serum hemagglutination-inhibiting antibodies in mice and to protect the animals against challenge infection with A/USSR/77 virus. Whole-virus and subunit virus vaccines were found to be equally efficacious, in contrast to our previous findings with vaccines prepared from other influenza virus strains. The effect of priming animals by infection with representative viruses of earlier eras on their response to A/USSR/77 vaccines was also studied. Enhanced responses were noted to both subunit and whole-virus A/USSR/77 vaccines in animals primed with viruses prevalent before 1957; higher antibody titers were induced with the subunit vaccine. A high degree of heterologous protection to A/USSR/77 challenge infection was found in mice primed with virus strains having hemagglutinin antigens unlike those of A/USSR/77 virus. Comparison of the responses of mice with those of humans inoculated with the same vaccines showed a similarity in many instances, with higher responses in those individuals primed with H0N1 and H1N1 viruses than in younger vaccinees.