A prospective, randomized, double-blind, placebo-controlled trial of WC/rBS oral cholera vaccine was conducted in 502 U.S. college students attending summer educational programs in Mexico.
Two doses of vaccine (or placebo) were administered 10 days apart immediately after arrival in Mexico.
The vaccine was free of significant adverse side effects. Anticholera toxin seroconversion was demonstrated in 86.7% of vaccinees compared to 8.2% of controls (p <.001). Postvaccination titers varied according to disease status (travelers' diarrhea) and enteropathogen isolated when disease developed. Protective efficacy (PE) against enterotoxigenic Escherichia coli (ETEC) diarrhea was 50% (95% Cl, 14–71 %), beginning 7 days after the second dose of WC/rBS. However, 74% of ETEC cases occurred within 7 days of the second dose, when no efficacy was demonstrated.
Vaccines employed to prevent travelers' diarrhea will likely need to be administered before arrival in a developing country to be predictably beneficial. An unexpected finding was that infection with LT-ETEC after primary oral cholera immunization appears to augment the antitoxin response to WC/rBS vaccine.