Return of epidemic A1 (H1N1) influenza virus.

Limited outbreaks of influenza were reported in the far east of the U.S.S.R. early in November, 1977, and a week or two later in cities in Siberia and the European parts of the U.S.S.R. The majority of influenza-virus isolates belonged to the H1N1 subtype of influenza-A virus, though strains of the current H3N2 subtype were also isolated. A moderate epidemic of H1N1 influenza spread throughout the country in the middle of December. Mainly children over 5 years and young adults were infected.