Data demonstrates that Shanchol™ (killed bivalent oral cholera vaccine) provides protection over 3 years and data regarding the protective efficacy over five years is anticipated for 2012. Regardless at the end of five years, it may still be necessary to provide a booster dose or reimmunize with two doses to maintain protection in previously immunized populations. This study examines the immune protection and safety of providing a one and two dose boosting regimen of Shanchol™ given five years after the initial dose.