[Study of the antigenic specificity of hemagglutinin of influenza viruses type A by quantitative radioimmunoassay. Comparative study of differences in the specificity of H3 hemagglutinin in epidemiologically active strains].

Comparative radioimmunoassays (RIA) of hemagglutinin of influenza type A viruses were carried out. The RIA was shown to detect definite type differences of influenza A and B virus hemagglutinin and subtype differences (HO and H3), as well as to determine both qualitative and quantitative characteristics of renewal of determinants within the antigenic drift. The A/Victoria/3/75 strain was found to have more renewed determinants than the A/Scotland/870/74 strain but less than the A/Victoria/112/76 strain which could be considered as a next drift variant. The epidemic strains circulating after 1972 had no more than 10% of the antigenic determinants characteristics of the original A/Hong Kong/1/68 strain. One of the advantages of the RIA was demonstrated to be its high sensitivity and economy as the specific antiserum can be used in dilutions 1:20,000 and higher. The test antigens may be both freshly isolated strains and virus-containing fluids showing no hemagglutinating activity (a titer in HA test 1:0).