Vaccine Adherence and Postvaccination Serological Status of Pediatric Allogeneic Hematopoietic Stem Cell Transplant Recipients: A Single-center Experience

Despite developing consensus guidelines addressing immunization after hematopoietic stem cell transplantation (HSCT), studies showed deviations from recommended immunization practices commonly occur. Difference between the ideal scenario presented in guidelines and real-life scenarios is one of the most recognized barriers to implementing recommended practices. Therefore, this study aimed to evaluate pediatric allogeneic HSCT recipients' adherence to revaccination schedule and evaluate the serological status after immunization. Transplant and vaccination records of children who were followed up at least 2 years after HSCT, postvaccination antibody results of vaccine-preventable diseases were evaluated retrospectively. Total of 173 patients have enrolled in this study. Median revaccination onset time was post-transplant 15 months. Adherence to revaccination program was 30% for inactive and 11.4% for live vaccines. Oral polio vaccine was given to 22 patients, and Bacille-Calmette-Guerin vaccine was applied to 3. Seropositivity after revaccination was >90% for Hepatitis B, Hepatitis A, pertussis, and measles, and it was 88.5% for rubella, 80% for mumps and varicella. Measles seropositivity was low in children with hemoglobinopathy. In subgroup assessments of pertussis, patients vaccinated with low antigen-containing pertussis vaccine (Tdap) had higher seropositivity of adenylate cyclase toxin. Our findings revealed the importance of careful monitoring of current practices in pediatric HSCT recipients.