[Humoral immunity to influenza A and B viruses in the blood sera of children younger than 14 in 1981].

Blood sera from 317 children with the history of noninfectious diseases or normal children pretreated with RDE were collected and examined for antihemagglutinins to 7 influenza virus strains in order to check the results of studies of 1980 and to study the immunity status to influenza A (H1N1), A (H2N2), A (H3N2) and B in the preepidemic period of 1981. Negative results of antihemagglutinin detection to influenza A/Iksha/1/57 (H2N2) in sera of all the children have confirmed the conclusion made in the previous paper (1) that influenza A (H1N2) viruses have not circulated in recent years among the population of Moscow City and suburban areas. Fourteen sera positive in HI tests with A/Shklyawer/49 virus similar to A/PR/8/34 (H1N1) in titres from 1:20 to 1:40 did not produce hemolysis zones with A/PR/8/34 virus in RHT, but most of these sera gave similar results of both tests with A/Brazil/11/79 and A/Khabarovsk/1/77 viruses. This attests to cross, nonspecific nature of hemagglutination-inhibition with A/Shklyawer/49 virus which evidently does not circulate now in the population of Moscow City and suburbs. An increase in the level of immunity to influenza B and A (H1N1)/1977 viruses reflected the epidemic situation of the previous year.