The purpose of the study was to assess the durability of humoral immunity in children with neoplastic disease 2.5 years after vaccination against hepatitis B virus. The study included 53 children divided into 3 groups, according to the method of passive-active prophylaxis. In group A first came passive prophylaxis during intensive chemotherapy, followed by the vaccination during supportive treatment; in group B children were vaccinated from the very beginning of chemotherapy with simultaneous administration of 2 doses of anti-HBs immunoglobulin; in group C patients received vaccination only after the completion of chemotherapy. Engerix-B vaccine was used for vaccination, and was administered in double doses, in regimen 0-1-2-8 months. Humoral response was evaluated in the 6th and 30th month following the fourth vaccination. After the vaccination cycle was completed, seroprotection was obtained in 66.7% of children in group A, 81.3% in group B and 100% in group C. Two and a half years after the termination of vaccination, all patients with primary seroconversion still possessed anti-HBs antibodies, while in two children the anti-HBs antibodies appeared after the discontinuation of chemotherapy. Anti-HBs antibody level increased in 45.3% of patients. Among patients who received the last dose of vaccine upon the completion of chemotherapy, as compared to those who received the last dose of vaccine during chemotherapy, we found a higher percentage of seroconversion to anti-HBs³10 IU/l (p<0.01) and higher mean arithmetic (p<0.05) in the 30th month after completion of vaccination. Geometric mean value of protective level of antibodies was in these patients more than two times higher. Long-term effects of vaccination in children with neoplastic disease reveal improvement of humoral response after the discontinuation of chemotherapy. More permanent results were obtained in children who received the last dose of the vaccine upon the completion of treatment.

Keywords: HBV infection, Vaccination, antibodies maintenance, children neoplasm