Five months after 2 siblings were immunized with varicella vaccine, 1 developed zoster. Two weeks later the second sibling got a mild case of chicken pox. Virus isolated from the latter was found to be vaccine type. Thus, the vaccine strain was transmitted from the vaccinee with zoster to his sibling. Vaccinees who later develop zoster must be considered contagious. varicella-zoster, zoster, vaccine, transmission, rash, PstI.