This study will last approximately 5 to 7 months with 25 study visits. Participants will be randomly assigned into one of two cohorts. Participants in Cohort 1 will receive an injection of rDEN2/4delta30(ME) or placebo vaccine at Days 0 and 180. Participants in Cohort 2 will receive an injection of rDEN2/4delta30(ME) or placebo vaccine at Days 0 and 120. Participants will be asked to record their temperature in a diary for 16 days after each vaccination. At each study visit a physical examination, symptom history, and blood and urine collection will occur.