Phase 1, randomized, double-blind, placebo controlled, dose-escalation, inpatient study of single doses of S. sonnei. Health adult subjects, ranging in age from 18 to 45 years of age (inclusive) will be screened. Enroll serial groups up to 90 subjects. The primary objective is to evaluate safety and tolerance of WRSs2 by monitoring presence, frequency and severity of clinical signs and symptoms. A secondary objective is to evaluate the immune response in blood and stool following ingestion of WRSs2 and WRSs3.