Volunteer studies investigating the safety and efficacy of live oral El Tor Vibrio cholerae 01 vaccine strain CVD 111

A live oral cholera vaccine should ideally protect against both classical and El Tor biotypes of Vibrio cholerae O1. An El Tor biotype vaccine strain, therefore, would complement classical cholera vaccine strain CVD 103-HgR, a strain already in use in some countries. In this study, 25 healthy adult volunteers received a single dose of 10(8) colony-forming units of Fl Tor vaccine strain CVD 111, a derivative of El Tor Ogawa strain N16117 deleted in the virulence cassette. Three (12%) volunteers developed mild diarrhea (mean stool volume = 813 mi) but no systemic symptoms; 23 (92%) of the 25 volunteers developed serum vibriocidal antibodies (geometric mean titer = 1:2,291). Five weeks after vaccination, 18 vaccinees and eight unimmunized control volunteers underwent wild-type challenge with Fl Tor Ogawa strain 3008. Three (16.7%) of 18 vaccinees and seven (87.5%) of eight controls developed diarrhea (P = 0.001) (vaccine efficacy = 80.9%). Further studies are underway to determine a dosage of CVD 111 that will be more clinically acceptable but equally immunogenic and protective.