Low levels of vaccine coverage and immunity against hepatitis B virus in children with hematological malignancies in Brazil.

Hepatitis B remains a global health concern due its high prevalence and association with chronic liver disease. Although vaccination is safe and effective in immunocompetent individuals, patients with hematological malignancies often exhibit immune dysfunction and reduced vaccine responses, increasing their susceptibility to vaccine-preventable infections. This study aimed to assess the hepatitis B vaccination status and immunoprotection in pediatric oncology patients treated at a tertiary public hospital in southern Brazil. A retrospective, single-center study was conducted with patients aged 0 to 15 years undergoing treatment for hematological malignancies between 2020 and 2022. Clinical and demographic data were obtained from electronic medical records, including vaccination history and hepatitis B serology profile. Vaccination status was verified through the National Immunization Program Information System. A total of 101 patients were evaluated, comprising 58 (57.4 %) males and 43 (42.6 %) females. The predominant diagnosis was acute lymphoblastic leukemia, reported in 67 cases (66.3 %). All patients underwent chemotherapy protocols, and 28 (27.7 %) died during the study period. Serological data for hepatitis B were available for 66 patients (65.3 %), with the highest proportions of missing data for anti-HBs (25.7 %) and total anti-HBc (13.9 %). None tested positive for HBsAg, 2 (2.3 %) were positive for total anti-HBc and 33 (44.0 %) for anti-HBs. Regarding vaccination status, 62 (61.4 %) had completed the hepatitis B vaccine series, 12 (11.9 %) had incomplete schedules, and 27 (26.7 %) had no records available. Only 10 patients (13.5 %) received additional vaccination after oncological diagnosis. Among those with a complete vaccination schedule, 27 (55.1 %) did not develop protective antibodies. These findings demonstrate low level of immunoprotection and suboptimal vaccine coverage against hepatitis B in this population. Optimizing vaccination protocols and monitoring strategies are essential to ensure adequate immunization against hepatitis B and other preventable diseases in immunosuppressed pediatric patients receiving care in Brazil.