Induction of Gut Permeability by an Oral Vaccine

Inclusion Criteria: * Body Mass Index (BMI) 18.5 - 29.9 kg/m2 Exclusion Criteria: * Has HIV/AIDS or another disease that affects the immune system * Has any kind of cancer * Decline to take an HIV blood test * Blood pressure greater than or equal to 140/90 mmhg * Pregnant or lactating women * Refusal to take a pregnancy test prior to the study * Refusal to use a method of birth control during the study * Allergy to vaccine components, i.e. Thimerosal and enteric-coated capsules * Allergy to oral typhoid vaccine * Allergy to aspirin * Daily use of blood thinners * Use of anti-inflammatory medications, i.e. nonsteroidal anti-inflammatory drugs (NSAID), aspirin, 3 or more times per month * Use of sulfonamides or antibiotics in the past 30 days * Use of anti-hypertensive drugs, i.e. beta blockers, diuretics, calcium channel blockers * Use of anti-malaria drugs, i.e. Mefloquine, chloroquine, and proguanil * Use of drugs that affect the immune system, i.e. immunosuppressants, immune-modifying drugs, corticosteroids, i.e. cortisone, prednisone, methylprednisolone, for 2 weeks or longer * Is taking cancer treatment with radiation or drugs * Greater than ten years residence in a typhoid-endemic area * Receipt of typhoid vaccine in the last 5 years * Receipt of any vaccine two weeks prior to receipt of Ty21a vaccine * Individuals at increased risk of developing complications from a live, bacterial vaccine * History of typhoid fever * History of primary immune deficiency or autoimmune disease * History of acute or chronic gastrointestinal (GI) disorder, i.e. Crohn's disease, irritable bowel syndrome, gastric ulcer * Diarrheal illness (defined as passing 3 or more abnormally loose or watery stool in a 24 hour period) or persistent vomiting 2 weeks prior to the study * History of bleeding disorder, including bleeding from the GI tract * History of chronic illnesses, i.e. diabetes, cardiovascular disease, cancer, gastrointestinal malabsorption or inflammatory diseases, kidney disease, autoimmune disorders, HIV, liver disease, including hepatitis B and C. * Asthma if taking medication on a daily basis * Recent surgery (within 3 months) * History of GI surgery * Recent hospitalization (within 3 months) * Acute febrile illness (within 2 weeks) * Unwillingness to discontinue consumption of artificial sweeteners in foods or drinks, i.e. sport drinks, coconut water, "diet" drinks and foods (possibly containing sucralose) * Not having at least one arm vein suitable for blood drawing * Unwilling or uncomfortable with blood draws seven times in 29 days * Regular blood or blood product donation and refusal to suspend donation * Current participation in another research study * Unable to fast for 12-16 hours