Protective Effect of Neonatal Hepatitis B Vaccine Against HBV Breakthrough Infection in Children with Leukemia: A Real-world Study

Background and Aims: Hepatitis B vaccine is the most ef-fective preventive measure against hepatitis B virus (HBV) infection. However, the risk of HBV breakthrough infection in fully immunized children (neonatal hepatitis B immuniza-tion) who receive immunosuppressive therapy and transfu-sion of blood components is not well characterized. In this real-world study, we aimed to investigate the immune pro-tection conferred by neonatal hepatitis B vaccine in children with acute lymphoblastic leukemia (ALL) who were treated with immunosuppressive therapy and blood component transfusions. Methods: Children with ALL who had received all three doses of neonatal hepatitis B vaccine were included in this study. HBV seromarkers were detected before and after the initiation of immunosuppressive therapy. Results: A total of 1,011 children with ALL who were fully vaccinated against hepatitis B in infancy before the initiation of im-munosuppressive therapy were eligible for inclusion. HBV infection was detected in four of 410 children (0.98%) with an HBsAg test after the initiation of immunosuppressive therapy. The median interval from treatment initiation was 19 months. Conclusions: Three doses of neonatal hepa-titis B vaccine conferred adequate protection. In endemic regions, there is a low risk of HBV breakthrough infection in fully immunized children with immunosuppressive therapy.