In double-blind trials in Bangladesh, 88 adults, and 79 children (8–10 years) were randomized to receive either a single oral dose of 1 × 104, 1 × 105 or 1 × 106 CFU of SC602 (a live, attenuated Shigella flexneri 2a strain vaccine) or placebo. In the adult outpatient 1 × 106 CFU group, severe joint pain and body aches were reported by one and two vaccinees respectively. In the adult inpatient trial, SC602 was isolated from 3 volunteers, pre-vaccination antibody titers were high, and fourfold increases in serum IgG anti-LPS responses were observed in 2 of 5 subjects of the 1 × 106 CFU group. None of the volunteers developed diarrhea. Overall, SC602 was found to be associated with minimal vaccine shedding, minimal reactogenicity, no transmission risk, and low immune stimulation.