Oral vaccination against enteric bacterial infections: an overview.

The present situation and the future prospects for the use of oral vaccines against the major enteric diseases typhoid fever, shigellosis and cholera are discussed in this paper. No significant protection could be demonstrated for oral inactivated whole-cell vaccines. In contrast, an oral live vaccine based on the attenuated Salmonella typhi strain Ty 21a was highly efficacious in volunteer challenge studies and in a controlled field trial. Two attenuated strains are presently being tested in volunteer studies as candidate vaccines against shigellosis; one uses S. typhi Ty 21a and the other Escherichia coli K-12 as the carrier for shigella antigens. Experimental challenge studies in volunteers showed that recovery from clinical cholera confers solid and long-lasting protection. The goal of present research is to develop a vaccine that mimics the events of clinical cholera without causing disease.