2\. Already scheduled to undergo an EGD or colonoscopy for screening, surveillance, or a medically-indicated work-up at the University of Maryland Medical Center (main campus or Midtown)
3\. Able to provide written informed consent prior to initiation of any study procedures
4\. Healthy, as defined by considered fit to undergo outpatient elective EGD/colonoscopy by the evaluating health care provider
You may not be if
1\. Pregnancy or nursing mother
2\. Known coagulopathy or bleeding disorder preventing mucosal biopsy
3\. History of Crohn's disease or ulcerative colitis
4\. For Subjects undergoing lower endoscopy (colonoscopy) only: Surgical removal of the ileocecal valve or any part of the small or large intestine (non-complicated appendectomy will be considered eligible)
5\. Allergic reaction to oral typhoid or cholera vaccine in the past
6\. Immunosuppression from illness or treatment, including
1. immune-deficiency disorders such as Human Immunodeficiency Virus (HIV) or Acquired Immunodeficiency Syndrome (AIDS)
2. leukemia, lymphoma, or cancers (localized non-melanoma skin cancers which are deemed inactive should be considered eligible)
7\. Receipt of any other vaccine two weeks prior to receipt of Ty21a or CVD 103-HgR
8\. Positive urine pregnancy test (HCG) prior to colonoscopy or vaccination
