RESUMEN
The etiology of an influenza outbreak which had occurred in Khabarovsk since 14 November, 1977 was elucidated. The largest number of cases was recorded among children and adolescents (under 22 years of age). Virological studies during the epidemic yielded 90 strains of influenza virus which were found to be antigenically quite close to A1 virus (HINI) which had circulated in this country in 1947-1956. Influenza viruses could be isolated from subjects under 22. Serological tests (H1, CFT) with paired sera from influenza patients and determinations of IgM showed A1 virus (HINI) to circulate more intensively among subjects under 22 years. A correlation between the presence of humoral immunity in subject over 22 and low incidence of influenza in these population are groups was observed.