Immunity in experimental cholera: effect of parenteral immunization with vaccines and toxoid.

The protection conferred by parenteral cholera vaccines and cholera toxoid was determined in the rabbit ileal loop model of experimental cholera. Vibrio cholerae strains belonging to two different serotypes were employed, for immunization and challenge, to differentiate antibacterial and antitoxic immunity patterns. It was found that vaccines were protective but cholera toxoid was not, although serum antitoxin levels were high after administration of the latter. Antibacterial immunity was strictly serotype-specific, with evidence of cross-protection only between Ogawa and Inaba subtypes of serotype 1. Bivalent serotype 1 vaccines conferred protection against homologous challenge strains but immunity to Inaba infection was of shorter duration than immunity to Ogawa infection.