[Analysis of the antigenic properties of strains of influenza virus that caused the epidemic of 1974-1975].

The etiology of influenza epidemic of 1974-1975 in the USSR was studied. The influenza viruses isolated from patients in the period of the 1974-1975 epidemic were tested in the hemagglutination-inhibition, neuraminidase activity-inhibition, immunoadsorption and biological neutralization tests. The majority of the strains tested were shown to be similar to the new antigenic variant A/Port Chalmers/1/73. It means that the strains of A/Port Chalmers/1/73 variant occurred epidemically in this region only in the winter of 1974-1975. The greatest differences between the new isolates and previously circulating strains of A/England/42/72 variant were observed in biologic neutralization tests.