CVD 909 Vi Prime Boost Study

Inclusion Criteria: * Age 18 - 40 years, inclusive. * Good general health as determined by a screening evaluation within 30 days before administration of CVD 909 or placebo. * Expressed interest and availability to fulfill the study requirements. * Informed, written consent. * Agrees not to participate in another investigational vaccine or drug trial for the first 84 days of this study. * Agrees not to become pregnant from the time of study enrollment until at least 56 days after the administration of CVD 909 or placebo; if a woman is sexually active and capable of conception (i.e., no history of hysterectomy or tubal ligation), she must agree to use hormonal or barrier birth control. A woman is eligible if she is monogamous with a vasectomized male. Exclusion Criteria: * History of any of the following medical illnesses: * Gall bladder disease or gall stones without cholecystectomy * Diabetes * Cancer * Heart disease (hospitalization for a heart attack, arrhythmia, or syncope) * Unconsciousness * Seizures (other than febrile seizures as a child less than 5 years old) * Recurrent infections (more than 3 hospitalizations for invasive bacterial infections such as pneumonia or meningitis) * Any current illness requiring daily medication other than vitamins, birth control, or stable regimen of anti-histamine medication for hay fever or anti-depressant * History of the following types of abdominal surgery: * Any major gastrointestinal surgery (e.g., intestinal resection or splenectomy) * A laparotomy for any reason (e.g., hysterectomy, Caesarean section, appendectomy, or herniorrhaphy) within the last 3 years * Laparoscopic abdominal surgery within the past year * A large abdominal scar of unclear origin * Evidence of gastrointestinal disease, as indicated by any of the following: * Usual bowel habit of more than 3 bowel movements each day * Recurrent diarrhea (greater than 5 episodes during the past 6 months, each lasting at least 3 days, with at least one week between episodes) * Lactose intolerance * Frequent indigestion or heartburn that requires daily antacids or other medical therapy * Diagnosed by a doctor as having irritable bowel disease, Crohn's disease, ulcerative colitis, celiac disease, stomach or intestinal ulcers in the past 10 years * Blood in the stool during the past year (other than occasional small amount from straining) * Any clinically significant abnormality detected on physical examination, including: * Murmur (other than a functional murmur) * Focal neurological deficit suggesting a pathologic process * Hepatosplenomegaly * Lymphadenopathy * Jaundice * Hypertension (BP greater than 150/90 mm Hg on two separate days) or hypotension (BP less than 85/55 mm Hg) * Any lab abnormality, as listed below: * WBC outside the normal range * Hemoglobin outside the normal range * Platelet count outside the normal range * Creatinine outside the normal range * Fasting glucose greater than 115 mg/dl (if screening greater than 115 mg/dl) * AST or ALT outside the normal range (may be repeated once if outside this limit) * Positive serology for hepatitis C or HIV antibody or hepatitis B surface antigen * Stool culture positive for Salmonella spp, Shigella spp, Campylobacter jejuni, V. cholerae, or pathogenic protozoa * For women, positive serum pregnancy test within 7 days and urine pregnancy test within 24 hours of administering CVD 909 and within 24 hours of administering Vi vaccine * Nursing mother * Oral temperature greater than 37.8ºC or symptoms of an acute self-limited illness such as an upper respiratory infection or gastroenteritis on the day of administration of CVD 909 or placebo * Immunization against typhoid fever or history of typhoid fever * Allergy to quinolones (including ciprofloxacin) or sulfa drugs (Including trimethoprim/sulfamethoxazole) * Medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 12 months * Failure to pass written examination about study purpose, background, and procedures (70% correct answers required to pass) * Receipt of an investigational vaccine or drug within 28 days before administration of CVD 909 * Commercial food-handlers * Health care workers who are engaged in patient care during the study * Day care providers * Subject with a household contact who is less than 2 years of age, who is immunocompromised or pregnant, or who works as a commercial food-handler * Use of antibiotics within 7 days of CVD 909 or placebo vaccination * Other condition that in the opinion of the investigator would jeopardize the safety or rights of a volunteer participating in the trial or would render the subject unable to comply with the protocol.