This study was a 5.5 year randomized, double-blind, placebo-controlled, efficacy trial to determine whether vaccination with live-attenuated Oka/Merck varicella-zoster decreases the incidence and/or severity of herpes zoster (HZ) and its complications in adults 60 years of age and older; 37,200 subjects over 60 years of age will be randomized at 22 sites to receive either vaccine or placebo. At least one third of the subjects were to be 70 years of age or older. Subjects were followed actively for HZ until at least 750 cases of HZ and at least 62 cases of PHN occurred. Subjects who developed HZ were evaluated for severity and duration of associated pain, extent and duration of rash, and for changes in quality of life associated with the disease for six months after the onset of HZ rash. All adverse events (serious and non-serious) occurring within 42 days after vaccination were recorded. Thereafter, serious adverse events were recorded if assessed as possibly related to the vaccination. An adverse event substudy was to enroll 6000 subjects for recording all adverse events on a vaccination Report Card. Substudy participants were also followed for any hospital admissions during the study.