Indications for varicella vaccination post‐transplant

Primary infection with varicella-zoster virus or chickenpox, has long been recognized as a serious and potentially life-threatening condition in children who are immunocompromised including those on immunosuppressive medication after solid organ transplant (1–4). In fact, children with leukemia in remission were among the first in North America to be immunized with the attenuated live varicella vaccine, in an effort to prevent the development of severe or fatal varicella infection in these children (5–7). It was only after such children were vaccinated safely and efficaciously that studies targeting healthy children were undertaken in the USA (5). The varicella vaccine has been approved and licensed in Japan and Korea since 1988, and in the USA since 1995. Its delivery to healthy children over the age of 12 months has been recommended by the AAP Committee on Infectious Diseases since 1995 and the ACIP of the Centers for Disease Control and Prevention since 1996 (8, 9). Because it is a live virus vaccine, both the AAP and ACIP recommend that the varicella vaccine not be given to certain immunocompromised children, including those receiving immunosuppressive therapy, status post-transplant (8, 9). These recommendations stem in part from findings of more extensive vaccine-associated rash or disseminated disease in children with acute lymphocytic leukemia vaccinated while on steroid therapy (10). The recommendation to avoid vaccination in immunosuppressed individuals has been reinforced by cases of severe reactions, including hepatitis, pneumonitis, and chronic herpes zoster in children with underlying immunocompromise or immunodeficiency which was not necessarily apparent at the time of immunization (11–15). Because of these recommendations, efforts to protect transplanted children from severe or fatal varicella infection has focused on immunizing varicella-naı̈ve children prior to the introduction of immunosuppressive medication post-transplant. In fact, this vaccine has been shown to be safe and immunogenic in children with chronic kidney failure, children on dialysis and children with chronic liver disease (16–19). It should be noted, that studies in children with chronic kidney disease suggested that two doses of the vaccine, rather than one, were required to achieve a 98% seroconversion rate, while the studies in patients with liver failure revealed 100 and 95% seroconversion after a single immunization in 29 and 44 children with chronic liver failure, respectively (15, 18, 19). Not only is this vaccine immunogenic, but in a large retrospective analysis, Broyer et al. (20) demonstrated a reduction in the incidence of varicella infection in pediatric kidney transplant patients after the routine administration of varicella vaccine was added to their pretransplant protocol in 1980. However, not all patients are able to receive the varicella vaccine prior to transplant. This is particularly true in liver and heart transplantation, as many children may require transplant of these organs in the first year of life, before the varicella vaccine may be given. In addition, studies of children vaccinated prior to transplant suggest that antibody titers to varicella-zoster virus may decline post-transplant, raising concern about the ability of the vaccine to provide long-term immunity in these children (16–18, 20). In those countries were the use of the varicella vaccine in healthy children has been widespread, such as Japan, Canada, Korea, Australia, Uruguay, Finland, and the USA, those who care for transplanted children can depend to some degree on herd immunity to reduce the risk of infection, by reducing the risk of exposure (5, 21–23). This is not the case in countries where varicella vaccine is not routinely recommended for healthy children, including many countries in Europe (21). Recently, The European Working Group Pediatr Transplantation 2005: 9: 141–144. DOI: 10.1111/j.1399-3046.2005. 00314.x