RESUMEN
In recent years notable advances have been made in the development of improved vaccines to prevent cholera. These new vaccines are administered orally to maximally stimulate intestinal secretory immunity. Killed vibrios, given in conjunction with purified B subunit or administered alone, in three spaced doses, caused no adverse reactions and have conferred significant protection in volunteer challenge studies and in field trials. Two attenuated mutants of V. cholerae, prepared by recombinant DNA techniques, CVD 103 and CVD 103-HgR are well-tolerated and elicit prominent immune responses and protective immunity after ingestion of a single oral dose. Other modern approaches being pursued include the development of auxotrophic strains and of modifying attenuated S. typhi strain Ty21a to express V. cholerae Inaba and Ogawa LPS antigens.