A subset of this group will be randomized to receive either a Typhoid Vi Polysaccharide Vaccine or Typhoid Vaccine Live Oral Ty21a vaccine in year 3. Each volunteer will complete a total of 4 visits for this immunization: Day 0 (pre-immunization), Day 6-8 post completion of injection or final oral dose, Day 12-15 and Day 26-30 (post-immunization). All visits will consist of drawing blood for study assays and monitoring for serious adverse events (SAEs).