Assessment of Antibody Levels and Vaccine-induced Serologic Responses After Completion of Cancer Treatment in Pediatric Patients: A 6-Year Experience in Turkey on HAV, HBV, VZV, and MMR Vaccinations.

Objective: Childhood cancer treatment disrupts vaccination schedules and weakens or eliminates vaccine-induced immunity. In addition, post-treatment vaccine responses vary. This study aimed to assess post-treatment serum antibody levels and vaccine responses in children.

Methods: Pediatric patients treated at Hacettepe University between years 2015 and 2020, achieved remission after chemotherapy for lymphoma and solid tumors were included. Post-treatment vaccination status, serum antibody levels for hepatitis A (HAV), hepatitis B (HBV), varicella-zoster (VZV), measles-mumps-rubella (MMR), and changes in vaccine responses were retrospectively analyzed.

Results: The study included 533 patients. Post-treatment seronegativity rates were: measles (83.5%), HAV (64%), rubella (60.1%), HBV (48.5%), VZV (43.3%), and mumps (28%). Post-treatment antibody loss was observed for measles (47.1%), HAV (31.9%), HBV (31.4%), mumps (28.6%), VZV (21.7%), and rubella (11.4%). Seropositivity after 1 vaccine dose was seen with HAV (83.6%), rubella (82.9%), HBV (81.4%), VZV (63.5%), mumps (45.4%), and measles (33.3%). Seropositivity after 2 vaccine doses was achieved with HAV (98.8%), VZV (84.6%), rubella (80%), HBV (80%), measles (32.2%), and mumps (36.2%).

Conclusion: Post-treatment serological vaccine responses in children were lower than anticipated despite multiple doses. Given the potential need for periodic serological assessments and booster vaccinations, long-term follow-ups are planned.