This study will enroll healthy adults with no history of previous infection with a flavivirus (any of a group of viruses that includes the dengue virus). Participants will be randomly assigned to receive either the TV003 vaccine or placebo vaccine on Day 0 (study entry). At Day 180, all participants will receive an injection of the "challenge" virus, rDEN2∆30, an attenuated (weakened) DENV-2 vaccine. For at least 30 minutes after each vaccination, participants will remain in the study clinic to be monitored for any adverse effects of the vaccines. Participants will record their temperature at least 3 times a day for 16 days after the first and second vaccinations.