[Importance of cross-reacting antibodies in creating resistance to influenza]

Hyperimmune rabbit serum to A/PR8/34 virus was analysed by selective adsorption of antibody by viruses belonging to hemagglutinin subtypes H0, H1 and Hsw1. The presence of three antigenic determinants was demonstrated in viral HA: one was common for HA of H0, H1, and Hsw1 viruses, the other was common for HA of H0, H1 and Hsw1 viruses, and the third was strain-specific for this virus. The protective effect of formalin-inactivated influenza vaccines prepared from virus variants with H0 and H1 hemagglutinins against challenge with A/PR8/34 virus was studied. The presence in the vaccine influenza virus of at least one antigenic determinant common with that of the challenge virus was shown to create a certain degree of protection in mice against influenza. The presence of two antigenic determinants in HA of vaccine and challenge virus increased considerably the protective effect of the vaccine.