*Purpose: International consensus guidelines to vaccinate children after transplant with varicella (VZV) vaccine exclude heart recipients due to insufficient evidence for safety, seroconversion rate, and adverse event profile. The purpose of this study is to report our novel early experience with VZV vaccination in children following heart transplantation (HTx).

*Methods: Single center, retrospective cohort study of pediatric HTx recipients who underwent VZV vaccination. Medical records were reviewed for demographic data, immunosuppression, immune testing, VZV IgG, and adverse events.

*Results: 31 children received at least 1 dose of VZV vaccine at a mean of 9 y post-HTx.(Table 1) 52% were on tacrolimus monotherapy; 42% were on tacrolimus/MMF. Table 2 summarizes vaccine-related data. Mean lymphocyte count was normal. CD3+CD4+ were on average low normal though a wide range. 21 children received 2 doses a median of 6.3 mos apart. 17 patients have had f/u serology: 16/17 (94%) VZV IgG+;13/14 (93%) VZV IgG+ at a mean of 6.3 mos after dose #2; 3/3 VZV IgG+ at a mean of 10.9 mos after dose#1. 10 (32%) patients experienced an adverse event (Table 3), most a rash at a mean of 18.7±6.1 d. Most were a few small raised red spots that self-resolved in 1-3 d; 1 was vesicular, 4 were pruritic. There were no major adverse events. 1 patient received anti-viral therapy early in the experience after a rash duration of 7 d (n=20 spots, no vesicles, no systemic symptoms).

*Conclusions: This is the first report in the literature of systematic live-attenuated VZV vaccination in a cohort of children following heart transplantation. Though consensus guidelines defer VZV vaccination in these patients and recommend caution in the setting of MMF use, the observations herein support that select pediatric heart transplant patients can be safely vaccinated with VZV vaccine with a 94% early seroconversion rate and a mild adverse event profile.

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