Participants will be randomly assigned to receive the rDEN3Δ30 vaccine or placebo at Day 0. Study visits will occur on Days 2, 4, 6, 8, 10, 12, 14, 16, 21, 28, 56, 90, and 180. Visits will include physical examinations and blood collection. All participants will record their temperature 3 times a day from Day 0 through Day 16. Some participants may be admitted to the clinic for an inpatient (overnight) stay during the first 16 days of the study.