This is an open-label, non-randomized study. Volunteers will be vaccinated with the typhoid oral vaccine, Vivotif. Vivotif has been licensed by the Food and Drug Administration (FDA) for travelers to developing countries. Volunteers will also be asked to provide blood, saliva, and stool specimens over a follow-up time period of up to eight years. The specimens obtained in this clinical research study will be used to further the investigator's understanding of the protective immunological mechanisms that can be elicited systemically and may be applicable to other enteric pathogens.