Evaluation of the Safety and Immunogenicity of Varivax® (Live-Attenuated Varicella-Zoster Virus Vaccine) in Pediatric Renal Transplant Recipients

Pediatric renal transplant patients face a lifetime of immunosuppressive therapy that place them at high risk for potentially life-threatening infection by primary varicella zoster virus (VZV). Treatment for acute episodes of VZV infection is possible but expensive and provides no long-term protection. Furthermore, therapy to overcome VZV infections can lead to renal graft rejection.

Varivax has proven safe, immunogenic, and effective in the normal host and has been recommended for universal administration in the general population at age 12 months. It is not currently labeled for use in immunocompromised patients. However, recent studies in pediatric leukemia and pediatric renal transplant patients suggest that attenuated live vaccine can confer protection with minimal adverse events even in the presence of immunosuppression, providing encouragement for more careful studies of VZV immunization in renal transplant patients. This study aims to quantify the safety and immunogenicity of Varivax in the population of pediatric renal transplant patients least susceptible to VZV infection, i.e., those on minimal maintenance immunosuppression and at least 1 year out from transplant.

Patient enrollment is staged to allow study physicians to closely monitor patients for signs of disseminated varicella reactions or graft rejection. Initially only 1 patient will be enrolled in the study. If the first patient reaches Week 8 without a severe adverse reaction, 3 study centers will then enroll 3 additional patients. If 8 weeks later these 3 patients have had no severe adverse reactions, the same 3 study centers will enroll 3 more patients. At the end of this period, having ascertained the safety of the vaccine in the first 7 patients, the study will be opened to the remaining centers. Patients receive 2 doses of Varivax 6 to 8 weeks apart. Each week for 6 to 8 weeks after the first vaccine dose, the patient undergoes venipuncture and clinical assessment to characterize renal graft and liver function and identify any signs of varicella infection. Additional telephone follow-up occurs on Day 4 and twice weekly thereafter. Parents or guardians monitor the patient for evidence of rash or fever and immediately report any rashes or fevers to study physicians. If, after 6 to 8 weeks, the patient demonstrates no severe reactions to the vaccine and requires no antiviral therapy, the patient receives the second vaccine dose. The patient again receives weekly on-site and telephone follow-up for 6 weeks. Other visits occur 9 weeks and 14 weeks after the second vaccine dose and 1 year after the first vaccine dose. At these visits the patient undergoes venipuncture and clinical assessment to identify potential rejection events or varicella infection and to characterize VZV antibody responses and cytokine changes in response to the vaccine.