Safety and Efficacy Study of CVD 1208S, a Live, Attenuated Oral Vaccine to Prevent Shigella Infection Using cGMP

Inclusion Criteria: * Age 18 to 45 years, inclusive. * Good general health * Expressed interest and availability to fulfill study requirements * Informed, written consent. * Agrees to indefinite storage of unused clinical specimens at the CVD for use in future research * Agrees not to participate in another investigational vaccine or drug trial during the study * Has no childbearing potential or agrees to abstain from becoming pregnant from the day of screening (at least 14 days before vaccination) until 6 weeks after the final vaccination by using birth control * Agrees not to donate blood to a blood bank for 12 months after receiving the vaccine. Exclusion Criteria: * An acute or chronic medical condition that, in the opinion of the investigator, would render vaccination unsafe or would interfere with the evaluation of responses. * Any current illness requiring daily medication (vitamins, birth control pills, nasal or topical medications, allowed); * Blood in stool on \>2 occasions (other than small amounts from straining) in past 12 months; * Recurrent diarrhea (\>5 episodes in past 6 months, each lasting 3 days or more). * Immunosuppression * Long term (greater than 2 weeks) use of oral or injected steroids, or high-dose inhaled steroids (\>800 micrograms/day of beclomethasone dipropionate or equivalent) within the preceding 6 months (Nasal and topical steroids are allowed). * History of abdominal surgery * Medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 12 months. * Known allergy or intolerance to ciprofloxacin, trimethoprim/sulfamethoxazole (or other sulfa antibiotic), ampicillin (for women) or corn. * History of shigellosis or Shigella vaccination or challenge or a laboratory worker with known exposure to Shigella. * Anticipates any of the following during the first 84 days (12 weeks) of the study (28 days, or 4 weeks for Cohort 1): * Shares a household with a child \<3 years of age, a pregnant woman or a woman who plans to become pregnant during this time; * Household or sexual contact with someone who has weakened immunity (such as someone with HIV infection, someone receiving treatment for cancer, or an elderly person \> 70 yrs); * Occupation as a food-handler, childcare (for children \<3 years), or health care worker with direct patient contact. * A clinically significant abnormality on physical examination * Results of blood tests as defined by protocol * Positive pregnancy test during medical screening or within 24 hours of inoculation or current breast feeding (women). * Failure to attain a score of at least 70% on the written examination (two attempts permitted) * During the past 3 years, developed diarrhea during travel to a developing country, or within 1 week of returning home. * Receipt of any of the following: * Any vaccine or investigational drug within 30 days of study vaccine * A live, attenuated vaccine within 30 days of the study vaccine * A subunit or killed vaccine within 14 days of the study vaccine * A blood product in the 90 days before the study vaccine * Receipt of antibiotics within 7 days of inoculation (or within 21 days if the antibiotic was azithromycin). * Loose stools or any other acute illness such as fever \>100.0 degrees F during the 48 hours before vaccination.