Preliminary assessment of the safety and immunogenicity of a new CTX Phi-negative, hemagglutinin/protease-defective El Tor strain as a cholera vaccine candidate

Vibrio cholerae 638 (El Tor, Ogawa), a new CTX Phi-negative hemagglutinin/p rotease-defective strain that is a cholera vaccine candidate, was examined for safety and immunogenicity in healthy adult volunteers. In a double-blin d placebo-controlled study, no significant adverse reactions were observed in volunteers ingesting strain 638. Four volunteers of 42 who ingested stra in 638 and 1 of 14 who received placebo experienced loose stools. The strai n strongly colonized the human small bowel, as evidenced by its isolation f rom the stools of 37 of 42 volunteers. V. cholerae 638, at doses ranging fr om 4 x 10(7) to 2 x 10(9) vibrios, elicited significant serum vibriocidal a ntibody and anti-Ogawa immunoglobulin A antibody secreting cell responses.