The study was initiated in December 1998. Patient recruitment began in November 1998 at one site, at 20 sites between February 1999 and July 1999, and at one site that was added in January 2000. On September 26, 2001, enrollment in the study was completed with 38,456 randomized subjects. The time point for the study definition of PHN was changed by protocol amendment from 30 days to 90 days after HZ rash onset. A formal sample size re-estimation was performed in June 2003. The Executive Committee and DSMB reviewed these results and approved the increase in event size from 400 to 750 evaluable cases of HZ for the primary endpoint. It was projected that the number of evaluable cases of HZ for the primary endpoint and the number of evaluable cases of PHN for the secondary (co-primary) endpoint would be observed by the end of September 2003. Therefore, the Study initiated its closeout plan beginning in October 2004. Follow-up of the last suspected case of HZ was completed in March 2004 and closeout interviews for the more than 37,000 surviving subjects were completed as of April 28, 2004.