[Level of antibodies to influenza viruses A and B in the blood sera of children under 13].

The level of antibodies to influenza A (H1N1), A (H2N2), A (H3N2), and B viruses in the blood sera collected in October and November, 1980, from 224 children under 13 resident in Moscow and its suburbs was studied The results of the study showed convincingly the influenza A (H2N2) viruses did not circulate at that time among the population of Moscow and its suburbs. The 4 positive (not exceeding 1 : 40 findings in sera from younger children were due to the presence in them of the antibodies cross-reacting with A (H2N2) and A H3N2) viruses which could be completely eliminated from the sera by adsorption of the latter with A/USSR/174/79 (H3N2) virus. The A (H3N2) viruses were the main cause of ARD developing in children in July-September, 1980. These diseases appeared to be the closing part of the influenza A (H3N2) epidemic of 1979-1980. A high percentage of children with antibody titres of 1 : 40 or higher to A (H3N2) viruses indicated that these viruses could hardly cause an epidemic of influenza in children in 1980-1981. A low percentage of children with serum antibodies to influenza B virus (1-10%) in titres of 1 : 40 or higher indicated a possibility of occurrence of an epidemic of this etiology in Moscow in the season of 1980-1981. The occurrence of influenza A (H1N1) epidemic in this period was less likely because of higher levels of antibody to influenza viruses of this subspecies in the sera of children and particularly adults.