Prepared or at-risk? Evaluating live viral vaccine coverage and vaccine immunogenicity before pediatric solid organ transplantation.

Pediatric solid organ transplant recipients are at high risk for complications from vaccine-preventable diseases, yet pre-transplant vaccination coverage is often inconsistent. We conducted a retrospective cohort study of 421 pediatric transplant recipients between 2018 and 2024 to evaluate vaccination status and serologic immunity for varicella and measles at the time of initial evaluation, listing, and transplantation. At the time of transplant, 19.2% of patients for varicella and 21.6% for measles were under-vaccinated, with infants having the highest rates of incomplete vaccination. A portion of patients (7.1% for varicella, 8.6% for measles) transitioned from full to incomplete vaccination status during the pre-transplant period, a change associated with a shorter time from evaluation to listing. Kidney recipients had the highest completed vaccination rates (>94%), whereas rates for liver and heart recipients were substantially lower (58%-72%). Among fully vaccinated patients, seronegativity was observed for varicella (23.6%) and measles (13.0%). In conclusion, many pediatric transplant candidates, particularly infants and those awaiting liver or heart transplant, are incompletely vaccinated. A dynamic change in vaccination status from evaluation to transplant highlights an urgent need for continuous monitoring and improved strategies to protect these vulnerable children.