The results of the main efficacy and safety analyses were unblinded on December 1, 2004, and presented to the DSMB, Executive Committee, and representatives for Merck & Co., Inc. Letters were sent to the study subjects informing them of the overall results and the treatment they received. The main manuscript was published in the New England Journal of Medicine (June 2005; 352:2271-84). The vaccine was approved for the prevention of shingles by the FDA on May 25, 2006. The main efficacy study is closed. Additionally, three substudies have been conducted: