Eligibility Criteria:
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