[Changes in antigenic determinant H3 in type A influenza virus]

The analysis of immune and hyperimmune rabbit sera to influenza A/USSR/0249/75. A/Victoria/3/75, and A/Tokyo/1/75 viruses showed the H3 antigenic determinant common for hemagglutinins of influenza viruses of the Hong Kong variety to be poorly manifest in viruses isolated in 1975 in contrast to type A viruses isolated in previous years. Antibody to the H3 antigen is usually absent in immune sera and appears only in hyperimmune sera after reimmunization of the animals. The quantitative decrease of the H3 antigen in viruses isolated in 1975 was also clearly detected in tests of adsorption of anti-H3 monoreceptor sera.