[Circulation of influenza A virus (H3N2) and its role in the occurrence of epidemics 1976-1981].

In 1976-1981 the etiology of influenza epidemics was mixed, influenza viruses A(H3N2), A(H1N1) and B taking part in them simultaneously. The active circulation of influenza virus strains with different antigenic structures was established: influenza virus A(H3N2) circulated in 1976, and since November 1977 simultaneous spread of influenza viruses A(H3N2) and A(H1N1) was observed, the epidemic activity of strain A(H3N2) being noticeably decreased during this period; in the autumn and winter months of 1979-1980 this strain appeared as the dominating infective agent. After intensive epidemics during the summer months of 1976 and 1980 influenza virus strains A(H3N2), antigenically related to the causative agent of the previous epidemic, were isolated from patients with acute respiratory infection. The cases of double infection with influenza viruses A and B were recorded.