A short-term persistence substudy (CSP#403A) was initiated in September 2004 to extend the follow-up vaccine and placebo recipients to assess the longer term effectiveness of the vaccine. This substudy bridged the period between the end of the efficacy study and the vaccination of placebo recipients and the initiation of a long-term persistence study. The study enrolled 14,270 subjects and completed follow-up in May 2007. This substudy is closed and is in ongoing analysis. The primary results for this study were published in Clinical Infectious Diseases (Clin Infect Dis. 2012 Nov 15;55(10):1320-1328)