Immunogenicity of two formulations of oral cholera vaccine comprised of killed whole vibrios and the B subunit of cholera toxin.

Two formulations of oral cholera vaccine were evaluated for safety and immunogenicity in adult volunteers in Thailand, an area with sporadic cholera outbreaks. One formulation consisted of 2 x 10(11) killed vibrios and 5 mg of cholera toxin B subunit, as was previously evaluated in North American volunteers, and the other consisted of 1 x 10(11) killed vibrios and 1 mg of B subunit, as was recently evaluated in a field trial in Bangladesh. Three doses of each formulation were given with citrate-bicarbonate buffer. Neither formulation had adverse effects. The formulations stimulated similar serum immunoglobulin G (IgG) and IgA responses to Vibrio cholerae lipopolysaccharide and cholera toxin and intestinal secretory IgA responses to lipopolysaccharide and toxin after three doses. The formulation containing twice the quantity of killed vibrios stimulated better vibriocidal responses, especially to Ogawa serotype. A formulation of oral vaccine containing more killed vibrios than were included in the vaccine studied in the Bangladesh field trial may provide greater protection against cholera.