Volunteer studies of typhoid fever and vaccines.

A series of studies evaluated the efficacy of three categories of typhoid vaccines: killed organisms given parenterally and orally and living attenuated mutants given orally. Vaccinees and unvaccinated controls were challenged with a single strain of virulent Salmonella typhi. Control individuals with prior military service (i.e. mandatory parenteral immunization) were significantly protected compared to non-veterans. Clinical protection of vaccinees was greatest (87%) following oral immunization with a mutant strain lacking epimerase.