Immunity Against Varicella in Pediatric Orthotopic Liver Transplantation Recipients

Varicella is a vaccine-preventable disease, which can be severe in immunosuppressed children. Currently, the (live) vaccine is not recommended in pediatric orthotopic liver transplant recipients. Furthermore, protection due to naturally acquired immunity to VZV or post-immunization isn't well described in this population.The questions asked are: * What is the influence of the immunosuppression required after orthotopic liver transplantation (OLT) on the maintenance of VZV-specific immunity elicited by wild-type varicella infection before OLT transplantation? * What is the influence of the immunosuppression required after OLT on VZV-specific immunity elicited by varicella immunization before OLT transplantation? * What is the influence of the residual immunosuppression at ≥ 12 months after OLT transplantation on the induction of VZV-specific B and T cell responses elicited by VZV vaccination after OLT transplantation? * What is the influence of the residual immunosuppression at ≥ 12 months after OLT transplantation on the persistence / waning of B and T cell responses elicited by VZV vaccination?