Eight subjects will return for redosing approximately 98 days after the initial dose, with the same inpatient and outpatient follow-up as above. Few or none should develop a diarrheal illness. Four naïve (previously unexposed) subjects will also receive the dose on Day 98 to confirm a 75% illness rate with this dose. They will be followed as the initial group was. All participants will be assessed by phone 6 months after the final dose they received.