Safety and immunogenicity of varicella-zoster vaccination in pediatric heart transplant recipients.

BACKGROUND

Pediatric heart transplant recipients are at increased risk of morbidity and mortality from vaccine-preventable infections due to long-term immunosuppression. Although live vaccines have traditionally been contraindicated post-transplant, emerging evidence supports their administration in selected solid organ recipients. This study evaluated the safety and immunogenicity of varicella-zoster virus (VZV) vaccination in pediatric heart transplant recipients.

METHODS

We retrospectively reviewed all pediatric heart transplant recipients who received a post-transplant VZV vaccination between November 2019 and April 2025 at our center. Baseline demographics, immune parameters, immunosuppressive regimens, serologic responses, and adverse events were analyzed in relation to the 2019 International Pediatric Transplant Association (IPTA) consensus guidelines.

RESULTS

Forty patients received at least one dose of VZV vaccination post-transplantation, of which 30 patients completed a two-dose vaccination series. Seroconversion was achieved in 97% of patients with eligible follow-up serology (n=36) and persisted in 80% at a median follow-up of 20 months. Adverse events occurred in 37.5% of patients, predominantly mild localized self-limiting rashes. One patient developed mild varicella, and one disseminated vaccine-strain VZV infection following re-transplantation shortly after vaccination. Notably, 53% were receiving mycophenolate mofetil, 25% had tacrolimus target levels of ≥ 8ug/mL, 55% had CD4 counts below age-specific reference, and 20% had detectable EBV loads.

CONCLUSIONS

Live-attenuated VZV vaccination appears safe and immunogenic in selected pediatric heart transplant recipients. These findings support cautious expansion of current vaccination criteria to include heart transplant recipients, those on MMF therapy, and patients with lower CD4 counts, with careful consideration of immunosuppressive stability at the time of vaccination.