[Results of a study of collective immunity to influenza A virus (H1N1) from 1976 to 1980].

The time course of the levels of circulating antihemagglutinins to influenza A (H1N1) virus in the populations of the towns in different geographical zones of the USSR was shown to be similar. The intensity of herd immunity in some areas differed considerably, however. The population of older age groups most of whom had no clinically manifest diseases during the influenza A (H1N1) epidemic was shown to experience immunological changes upon exposure to this agent. The intensity and the rate of changes in the immunological structure of this portion of the human population exceeded similar parameters among the subjects under 20 years of age who had experienced manifest forms of infection. Some people with immunological memory to influenza A (H1N1) virus developed antibody in response to infection or immunization with influenza A (H3N2) strains.