Results of a two-year study of humoral immunity to influenza A and B viruses in children under the age of 14 years in Moscow and its suburbs.

A serological survey of antibodies to influenza A(H1N1), A(H2N2), A(H3N2) and B viruses was done with sera collected in Moscow in October 1980 and November 1981 from 542 children under 14 years of age. The results of the study showed convincingly that influenza A(H2N2) viruses were not circulating in Moscow in 1980-81. Low titres found in the sera from four young children were due to cross-reactions which were eliminated from the sera by absorption with A/USSR/174/79(H3N2) virus. Low-level HI titres with A(H0N1) virus in 11 sera were not confirmed by single radial haemolysis (SRH).Serological data showed that A(H3N2) viruses were the main cause of acute respiratory disease in children in July-September 1980 and July-September 1981. These illnesses occurred at the end of the influenza A(H3N2) epidemic of 1979-80 in the third quarter of 1980. The influenza A(H3N2) virus circulated in Moscow during December 1981 and January 1982, but influenza did not reach epidemic levels. A low proportion (10%) of children with antibodies to influenza B virus at titres of 1:40 or higher in 1980 indicated the possibility of an epidemic due to this virus in Moscow in 1980-81. Such an epidemic did occur in December 1980 and January 1981.