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Introduction: live attenuated oral Vibrio cholerae Ol El Tor, Ogawa strain 638 has demonstrated to be well tolerated and immunogenic when administrated orally in studies carried out in healthy volunteers., Objectives: to evaluate the protection against cholera infection in a challenge clinical trial, for the technological and pharmaceutical scale-up of this vaccinal candidate as active ingredient at industrial level., Methods: a total of 21 healthy volunteers were involved in this trial; the vaccine candidate was administered to 12 of them and the remaining nine were given the placebo. Twenty eight days later, all of them received an infective dose of a V. cholerae virulent strain., Results: diarrheas were observed in 7 out of 9 placebos whereas not a single vaccinated volunteer showed diarrheas. More frequent and intense loose stools were found in the placebo volunteers with O-blood group. All volunteers in he placebo group excreted V. cholerae, but only three (25%) out of the 12 vaccinated volunteers did so., Conclusion: in this challenge clinical trial model, the 638 strain proved to protect people against the diarrhea caused by a virulent V. cholerae strain.