Correlated Studies of a Recombinant Influenza-Virus Vaccine. II. Definition of Antigenicity in Experimental Animals

Abstract

The present experiments were designed to assess the immunogenic properties of an inactivated influenza-virus vaccine made from a recombinant virus (X-31) that possesses the surface antigens of Aichi virus and the growth capacity in eggs of A₀/PR8 virus. Antibody response in mice and rabbits was tested by assay for titers of hemagglutination inhibition, plaque inhibition, plaque-size reduction, and neuraminidase inhibition following immunization with graded doses of the recombinant vaccine and a standard Aichi virus vaccine of equivalent antigenic content, as determined by the chick-cell-agglutination test. The X-31 vaccine was slightly more effective in eliciting antibody to hemagglutinin in both rabbits and mice and was also more effective than Aichi vaccine in increasing the resistance of mice to the initiation of infection with Aichi virus. Similar titers of antibody to neuraminidase were elicited by the two vaccines, and both were more potent in stimulating antibody to hemagglutinin than to neuraminidase. The results indicate that the recombinant vaccine was at least as effective as a standard vaccine in its immunogenic properties. In addition, the results of these experiments raise questions regarding the accuracy of the chick-cell-agglutination test as a method for assaying immunogenic potency.