Live attenuated varicella vaccine: protection in healthy adults compared with leukemic children. National Institute of Allergy and Infectious Diseases Varicella Vaccine Collaborative Study Group

Protection against varicella infection was assessed in leukemic children and healthy young adults who were immunized with live attenuated varicella vaccine. Attack rates of breakthrough infection following household exposure to varicella in 102 children and 26 adults were similar whether one or two doses of vaccine had been given. The mild breakthrough illness was also similar after one or more doses. Specific antibody titers were similar 1 year after immunization whether individuals had received one or two doses. Humoral and cell-mediated immunity to varicella-zoster virus (VZV) was lower in these vaccinees than in persons who had experienced natural varicella infection. Protection after natural infection in adult family members exposed to varicella was superior to that in vaccinees; none developed varicella infection. These observations suggest that immunization induces less protection than does natural disease in leukemic children and young adults. This may be partly due to the nature of the vaccine virus, but because responses of adults were similar to those of leukemic children, it suggests also that both of these groups have impaired immune responses to VZV. Boosting of humoral immunity after exposure to VZV was common and was observed in healthy adults with past natural infection and in vaccinated adults and leukemic children.