Dengue fever, which is caused by dengue viruses, is a major health problem in tropical and subtropical regions of the world. The purpose of this study is to test the safety of and immune response to a new dengue virus vaccine in healthy adults.

More than 2 billion people living in tropical and subtropical regions of the world are at risk of dengue virus infection. Dengue viruses cause dengue fever, as well as the more severe dengue hemorrhagic fever/shock syndrome, and dengue virus infection is the leading cause of hospitalization and death in children in several tropical Asian countries. This study will evaluate the safety and immunogenicity of a live, attenuated dengue virus called rDEN1delta30, which is derived from the Western Pacific DEN1 serotype.

This study will last 180 days. Participants in Cohort 1 will be randomly assigned to receive rDEN1delta30 or placebo at study entry. Cohort 2 will begin only after safety review of all participants in Cohort 1. Participants in Cohort 2 will receive a higher dose of rDEN1delta30 or placebo.

After vaccination, participants will be asked to monitor their temperature every day for 16 days. Study visits will occur every other day after vaccination until Day 16, followed by 4 additional visits at selected days through Day 180. Blood collection and a targeted physical exam will occur at each study visit. Some participants will be asked to undergo a skin biopsy or additional blood collection at selected visits.

Inclusion Criteria:

• Willing to be followed for the duration of the study
• Willing to use acceptable methods of contraception
• Good general health

Exclusion Criteria:

• Clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, or renal disease
• Behavioral, cognitive, or psychiatric disease that, in the opinion of the investigator, affects the ability of the volunteer to understand and cooperate with the study
• Liver, renal, or hematologic disease
• Alcohol or drug abuse within 12 months of study entry
• History of severe allergic reaction or anaphylaxis
• Emergency room visit or hospitalization for severe asthma within 6 months of study entry
• HIV-1 infected
• HCV infected
• Hepatitis B surface antigen positive
• Known immunodeficiency syndrome
• Use of corticosteroids or immunosuppressive drugs within 30 days of study entry. Participants who have used topical or nasal corticosteroids are not excluded.
• Live vaccine within 4 weeks of study entry
• Killed vaccine within 2 weeks of study entry
• Blood products within 6 months of study entry
• Investigational drugs or vaccines within 60 days prior to study entry or while currently enrolled in this clinical trial
• Previously received a licensed or experimental yellow fever or dengue vaccine
• Surgical removal of spleen
• History of dengue virus infection or other flavivirus infection
• Other condition that, in the opinion of the investigator, would affect the participant's participation in the study
• Pregnancy or breastfeeding
• Plan to travel to an area where dengue infection is common