Safety and immunogenicity of live-attenuated measles-mumps-rubella vaccination after pediatric heart transplantation

In recent years, global outbreaks of measles and mumps have re-emerged as herd immunity declines. Pediatric heart transplant recipients are at increased risk for severe vaccine-preventable infections, yet live vaccines have historically been avoided due to safety concerns. Data on post-transplant measles-mumps-rubella (MMR) vaccination remain limited.

We conducted a retrospective single-center cohort study of pediatric heart transplant recipients who received live-attenuated MMR vaccination between January 2022 and January 2026 under a structured post-transplant vaccination protocol. Eligibility required clinical stability, >6 months post-transplantation, no recent rejection, and predefined immune parameters. Safety, immunosuppressive status, and serologic response were assessed.

Twenty-nine recipients received 49 MMR doses at a median of 9.8 years post-transplant. Vaccination was well tolerated, with no vaccine-related adverse events, rejection episodes, or graft complications. Post-vaccination serologic data were available for 23 recipients. Overall seroconversion rates were 61% for measles, 65% for mumps, and 100% for rubella, with higher measles responses after 2 doses (68% vs 43%). Seroconversion was not associated with age, time from transplantation, immunosuppression, or immune parameters. Most patients (65%) would not have met 2019 IPTA criteria for standard live vaccination eligibility.

In carefully selected pediatric heart transplant recipients, MMR vaccination was safe and provided acceptable immunogenicity. These findings challenge the historical exclusion of this population from live vaccination and suggest current eligibility criteria may be overly restrictive.