Immunogenicity and Safety of Live Attenuated Varicella Vaccine in Children and Youth With Solid Organ Transplants in Canada: A Canadian Immunization Research Network Study

INTRODUCTION: Children with solid organ transplants (SOT) face higher risks of severe disease from varicella-zoster virus (VZV). Although some guidelines recommend live attenuated varicella vaccine (LAVV) for select children post SOT, further real-world vaccine immunogenicity and safety data are needed. METHODS: A prospective observational study was conducted at 4 Canadian centres from 2020 to 2023. Children who were 1-19 years, VZV IgG negative, > 1 year post liver, kidney, or heart transplant, and were receiving LAVV as part of clinical care in accordance with centre-specific criteria were eligible for inclusion. Measurement of VZV IgG was recommended post-vaccination with LAVV. Adverse events following immunization (AEFIs) were captured via telephone survey and chart review. RESULTS: Fifty-six pediatric SOT recipients (51 liver, 3 kidney, and 2 heart) received ≥ 1 dose of LAVV. Serology after the last post-transplant dose of LAVV was available for 43/56 (77%) participants; 39/43 (91%) seroconverted to positive VZV IgG (12/16 after 1 post-transplant dose, 26/30 after 2 doses and 1/1 after 3 doses). Among 56 dose 1 recipients, 6 (11%) experienced an AEFI requiring medical attention. Four had rash: 3 with varicella-like rash (1/3 confirmed vaccine-strain varicella) and none required antivirals. Two had acute rejection 4-5 weeks after LAVV. Two of 38 (5%) dose 2 recipients had an AEFI requiring medical attention, with one serious AEFI 7 weeks after LAVV that was not deemed vaccine-related after careful review. CONCLUSIONS: LAVV was immunogenic and generally well tolerated in our cohort of patients. Post-SOT LAVV should be considered for select VZV seronegative children with close follow-up.