Long-term Seroprotection of Varicella-zoster Immunization in Pediatric Liver Transplant Recipients

Background. Chickenpox is a highly contagious vaccine-preventable disease that can lead to severe complications, especially in immunocompromised patients. Varicella-zoster virus (VZV) vaccine appears to be safe and immunogenic in pediatric solid organ transplant recipients, but there are few data on the long-term vaccine-induced seroprotection. Methods. In this prospective interventional study, we offered 2 doses of VZV vaccine to all eligible and nonseroprotected children seen 1 year after liver transplant. Vaccine responses were measured 1 month later and yearly thereafter. Vaccine safety was closely monitored. A supplementary dose was administered if protective levels were not reached/maintained. Results. Among 121 enrolled patients, 49 were vaccinated and followed during 5.5 years (interquartile range, 3.7-8.0). Their seroconversion rate reached 100% (97.5% confidence interval [CI], 92.7-100). Low VZV-antibody concentration (<= 400 UI/L) after the first 1-2 dose/s was associated with the need for a supplementary dose (odds ratio, 15.0; 95% CI, 3.4-67.0, P = 0.001) and was given to 31% (15/47) of children at 1.1 year (interquartile range, 0.9-3.9). Although antibody concentrations declined during follow-up, 96% (95% CI, 86.0-99.5) of patients maintained protective antibody concentrations at a median of 5.5 years after vaccination. One breakthrough disease was identified. Conclusions. VZV immunization of pediatric solid organ transplant recipients confers sustained seroprotection.