Evidence that inactivated oral cholera vaccines both prevent and mitigate Vibrio cholerae Ol infections in a cholera-endemic area

In a randomized, placebo-controlled field trial of B subunit-killed whole cell (BS-WC) and killed whole cell only (WC) inactivated oral cholera vaccines in rural Bangladesh, active surveillance of selected neighborhoods during the first year after vaccination identified 127 Vibrio cholerae O1 infections among 3285 three-dose recipients. For each vaccine, protective efficacy was greater against symptomatic (57%, P <.05 for BS-WC; 58%, P <.05 for WC) than against asymptomatic infections (46%, P <.05 for BS-WC; 32%, P =.09 for WC), and protection against each grade of infection was demonstrable for both the classical and E1 Tor biotypes. Although vaccine protection against symptomatic infections was evident in both young children and older persons, only persons vaccinated at age >5 years were protected against asymptomatic infections. These results suggest that the inactivated oral vaccines acted both to protect against intestinal colonization by V. cholerae O1 and to interrupt the pathogenic sequence of established infections.