Objective: Our aim was to evaluate the child and adolescent population immunity to influenza A viruses (IAV) and influenza B virus (IBV).
Methods: The concentration and specificity of antiviral antibodies was evaluated by hemagglutination inhibition assay (HAI) that was performed using commercial HAI diagnostic kits.
Results: The serum samples of 254 clinically healthy children and adolescents were examined in this study. 245 participants had the antibodies to IAV, 199--to IAV and IBV and only 4 children aged between 1 and 4 years and a 12-year-old boy had no immunity to IAVor IBV. The number of children with specific immunity increased in elder groups by 43% (from 81 to 116) for N0N1, and H3N2 subtypes and by 110% (from 38 to 80) for H1N1 subtype of IAV. In children younger than 4 years the titer of specific antibodies against the H1N1pdm09 was 1:210 and against the H3N2--1:270, whereas in adolescents of 10-14 years these figures were by 1.6 and 2.4 times lower (1:130 and 1:120) respectively. Antibodies to the subtypes H2N2 and H5N1 were not detected.
Conclusion: The results indicate that 98.4% of child and adolescent population in interepidemic influenza season are immune to the various IAV (H3N2, H1N1, H0N1) as well as to the IBV. More than half of children and adolescents (57.4%) are immune to H1N1pdm09 subtype of IAV. The strength of immune response to the recent pathogens (H3N2 u H1N1pdm09) is higher in infants than in teenagers.