We hypothesize that children listed to undergo solid organ transplant will experience (at the very most) a low rate (< 5%) of serious vaccine-related adverse events within 42 days after immunization with live attenuated Oka/Merck varicella vaccine (VARIVAX™). We also hypothesize that the immunogenicity of two doses of VARIVAX™ in the study population will be similar to historical data in healthy subjects and that the efficacy of two doses of the vaccine in the study population will be similar to that of healthy subjects.