Background: Vaccination for hepatitis B virus (HBV) after chemotherapy among pediatric patients with acute leukemia is still a debated issue. We investigated HBV immunity before and after chemotherapy and assessed immune response to re-vaccination after chemotherapy.  Methods:  We retrospectively analyzed data of children and adolescents aged <19 years requested for vaccination after chemotherapy for acute leukemia to evaluate hepatitis B surface antibody (HBsAb) status before and after chemotherapy and to identify factors related to HBsAb positivity after chemotherapy. Results:  Of 89 enrolled patients, 61 (68.5%) with acute leukemia were HBsAb positive before chemotherapy. Of these 61 patients, 48 (78.7%) seroconverted to HBsAb negative status after chemotherapy; there were 76 (85.4%) HBsAb negative patients after chemotherapy. HBsAb positive patients when compared to HBsAb negative patients after chemotherapy had a significantly higher HBsAb positive rate (100.0% vs. 63.2%, p=0.008) before chemotherapy. Following HBsAb testing after one dose of the HBV vaccination, 33 (43.4%) of the 76 HBsAb negative patients seroconverted to a HBsAb positive status. HBsAb positive patients after a single dose of HBV vaccination had a significantly higher HBsAb positive rate at the time of diagnosis compared to HBsAb negative patients (84.8% vs. 48.8%, p=0.001). Conclusions:  Based on these results, HBV re-vaccination after chemotherapy is recommended for all children and adolescents with acute leukemia. In addition, further investigation is required to improve the immunogenicity of HBV re-vaccination.   Keywords: Acute Leukemia; Chemotherapy; Hepatitis B vaccine; Hepatitis B virus; Child.

The results showed inferior immunogenicity of the new DTaP vaccine compared to a commercial vaccine despite comparable cellular immunity and protective efficacy. Some efforts are necessary for improving immunogenicity against filamentous hemagglutinin and pertactin before conducting human clinical trials.

The new Td vaccine is highly immunogenic and safe, and this new Td vaccine can be effectively used for preventing diphtheria and tetanus.

A multicenter, double-blind, randomized, active-control phase III clinical trial was performed to assess the immunogenicity and safety of a trivalent, inactivated split influenza vaccine. Korean children between the ages of 6 months and 18 y were enrolled and randomized into a study (study vaccine) or a control vaccine group (commercially available trivalent, inactivated split influenza vaccine) in a 5:1 ratio. Antibody responses were determined using hemagglutination inhibition assay, and post-vaccination immunogenicity was assessed based on seroconversion and seroprotection rates. For safety assessment, solicited local and systemic adverse events up to 28 d after vaccination and unsolicited adverse events up to 6 months after vaccination were evaluated. Immunogenicity was assessed in 337 and 68 children of the study and control groups. In the study vaccine group, seroconversion rates against influenza A/H1N1, A/H3N2, and B strains were 62.0% (95% CI: 56.8–67.2), 53.4% (95% CI: 48.1–58.7), and 54.9% (95% CI: 48.1–60.2), respectively. The corresponding seroprotection rates were 95.0% (95% CI: 92.6–97.3), 93.8% (95% CI: 91.2–96.4), and 95.3% (95% CI: 93.0–97.5). The lower 95% CI limits of the seroconversion and seroprotection rates were over 40% and 70%, respectively, against all strains. Seroconversion and seroprotection rates were not significantly different between the study and control vaccine groups. Furthermore, the frequencies of adverse events were not significantly different between the 2 vaccine groups, and no serious vaccination-related adverse events were noted. In conclusion, the study vaccine exhibited substantial immunogenicity and safety in Korean children and is expected to be clinically effective.