Antibodies to the strain-specific and cross-reactive determinants of the haemagglutinin of influenza H3N2 virus. 3. Selection of antigenic variations in vitro and in vivo.

Antigenic variants of influenza A/Hong Kong/1/68 (H3N2) were obtained in vitro by letting virus multiply in the allantosis-on-shell system in the presence of anti-haemagglutinin antibodies, prepared from immune goat serum to purified haemagglutinin antigen, and in vivo by giving mice antibody intraperitoneally one day before challenge with a sublethal dose of live virus. In both systems it was shown that the most narrowly reacting strain-specific antibodies selected antigenic variants at an apparently higher rate than a more cross-reactive preparation of antibodies.