Evaluation of post-treatment vaccine serological responses and vaccination program in children with cancer receiving chemotherapy

Objective: Childhood cancer causes failure to complete the childhood vaccination program and weakening/loss of immunity acquired with vaccination due to immunosuppressive treatments. Because of this, pediatric cancer survivors have been completely vulnerable to vaccine-preventable diseases. It is known that the post-treatment vaccine responses of children receiving cancer treatment also vary. There is no international common guideline on vaccination in children after cancer treatment. This study planned to examine serum antibody status, administered vaccines, and vaccine responses after cancer treatment. Methods: Children and adolescents who applied to Hacettepe University Faculty of Medicine, Department of Pediatrics, Social Pediatrics clinic between 2015-2020, received chemotherapy with the diagnosis of lymphoma and solid organ tumors, were in remission, and applied for vaccination plan and follow-up were evaluated. Vaccines administered after cancer treatment and hepatitis A (HAV), hepatitis B (HBV), varicella zoster (VZV), measles-mumps-rubella (MMR) serum antibody levels, and vaccine responses were retrospectively analyzed. Results: Of the 533 patients included in the study, 304 (57%) were male, 229 (43%) were female (M/F: 1.3), mean age at diagnosis (±SD) was 5 years 10 months (±57 months). The most common diagnoses were Non-Hodgkin lymphoma (NHL) (15.4%), central nervous system (CNS) tumors (13.1%), and Hodgkin lymphoma (HL) (12%). The number of patients who received at least one dose of vaccine after treatment was 508 (95.3%). The age of diagnosis of 52.9% of the patients was 0-5 years and childhood vaccinations were missing, 26.8% of the patients were diagnosed at 0-2 years of age, and infancy vaccines were missing. Post-treatment vaccines were mostly pneumococcal conjugate vaccine (PCA) (85.4%), MMR (80.7%), and HBV (66.8%). Post-treatment, a lack of protective antibody titers against HAV, HBV, VZV, and measles-mumps-rubella was detected in 64%, 48.5%, 43.3%, 83.5%, 28%, and 60.1% of patients, respectively. In patients who were known antibody titers pre-treatment and after treatment for HAV, HBV, VZV, and measles-mumps-rubella, the loss of antibody titers was found in 31.9%, 31.4%, 21.7%, 47.1%, 11.4%, and 28.6% of patients, respectively. Patients with known antibody titers status before and after treatment, HAV, HBV, VZV, and measles-mumps-rubella antibody loss, respectively; It was found to be 31.9%, 31.4%, 21.7%, 47.1%, 11.4%, and 28.6%. It was determined that 83.6%, 81.4%, 63.5%, 33.3%, 82.9%, and 45.4% of the patients developed seroconversion to one dose of HAV, HBV, VZV, measles-mumps-rubella vaccine, respectively. It was determined that 98.8%, 80%, 84.6%, 32.2%, 80%, and 36.2% of the patients developed seroconversion to two doses of HAV, HBV, VZV, and measles-mumps-rubella vaccine, respectively. Conclusion: Vaccination is the most effective method developed against infectious diseases. Pediatric cancer patients who underwent chemotherapy lost immunity against vaccine-preventable diseases. The long-lasting side effects of chemotherapy on the immune system cause variability in the vaccine responses of patients after treatment. Keywords: Childhood cancers, chemotherapy, vaccination, antibody response