[Changes in the indices of the immunogenic activity of influenza A/Hong Kong virus in the 1969-1980 epidemics].

The study of immunological changes in convalescents after influenza aged 7-12 months and 18-23 years was carried out in the period of circulation of influenza A/Hong Kong virus and its antigenic variants (1969-1980). A continuous decrease of the immunogenic activity of the causative agents of repeated epidemics and the intensity of the acquired immunity in adult convalescents was demonstrated in successive epidemics of influenza A/Hong Kong. This regularity was fully confirmed in groups of 7 - 12-month-old infants without previous exposure to influenza infection who experienced the disease. Marked differences in the incidence and clinical severity of earlier and later epidemics of influenza A/Hong Kong and changes in immunogenic activity suggest that they are associated with different virulence of the causative agents at different periods of a general pandemic cycle.