Safety and immunogenicity of a live oral bivalent typhoid fever (Salmonella typhi Ty21a)-cholera (Vibrio cholerae CVD 103-HgR) vaccine in healthy adults.

The safety and immunogenicity of the live oral attenuated vaccine strains vibrio cholerae CVD 103-HgR and Salmonella typhi Ty21a were evaluated alone or in a combined bivalent formulation in four groups composed of 185 healthy European adults. All presentations were well tolerated. The serum anti-S. typhi lipopolysaccharide immunoglobulin G and immunoglobulin A antibody responses were comparable for all groups (66 to 72% seroconversion). The serum vibriocidal antibody seroconversion rate ranged from 78 to 92.5% (P > 0.05) among the groups. However, the peak and geometric mean vibriocidal antibody titers were significantly higher (P < 0.005) in the groups which received the bivalent formulation along with two doses of Ty21a than in the group which received CVD 103-HgR followed by two doses of killed Escherichia coli K-12 placebo. The ingestion of a placebo shortly after CVD 103-HgR may have suppressed the magnitude of the immune response. These findings demonstrate the feasibility of producing multivalent live oral attenuated vaccines.