Immunization of Healthy Adults with Live Attenuated Varicella Vaccine

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Abstract
Live attenuated varicella vaccine was administered to healthy varicella-susceptible adults. Of 187 adults immunized with the Oka strain of vaccine, seroconversionto varicella-zoster virus (VZV) occurred in 82% after one dose and in 94% after two doses. Adverse effects were unusual. After immunization au]one subject developed mild zoster caused by wildtype virus. Twelve adults developed a mild breakthrough case of chickenpox after exposure to VZV. Protection after household exposure was observed in nine (56%) of 16; however, the illness in all seven patients with breakthrough illness was modified, with an average of only 24 vesicles. Subjects seropositive at household exposure were unlikely to develop a breakthrough illness. Approximately 25% of vaccinees who seroconverted lost detectable antibodies to VZV after vaccination, but even those who became seronegative were partially protected. Varicella vaccine offered significant protection against severe chickenpox in healthy adults.