Infection is a major cause of morbidity and death among haemopoietic stem cell transplantation patients (HSCTs). Beyond the initial post-transplant (BMT) phase of neutropenia, the most common infections are cytomegalovirus (CMV) and fungal infections. Another common infection for which BMT patients are at increased risk is varicella-zoster virus (VZV) (both primary varicella and herpes zoster). VZV infection is controlled by specific T cell responses that are impaired post stem cell transplant.