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.

Dengue viruses cause dengue fever, as well as the more severe dengue hemorrhagic fever/shock syndrome. More than 2 billion people living in tropical and subtropical regions of the world are at risk of dengue virus infection, which 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 vaccine called rDEN2/4delta30(ME), which is derived from the DEN2 and DEN4 serotypes.

This study will last 180 days. Participants in Cohort 1 will be randomly assigned to receive rDEN2/4delta30(ME) 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 rDEN2/4delta30(ME) or placebo.

After vaccination, participants will be observed for at least 30 minutes for immediate adverse reactions. Participants will also 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
• Hematologic disease
• Alcohol or drug abuse within 12 months prior to study entry
• History of severe allergic reaction or anaphylaxis
• Emergency room visit or hospitalization for severe asthma within 6 months prior to study entry
• HIV-1 infected
• Hepatitis C virus infected
• Hepatitis B surface antigen positive
• Known immunodeficiency syndrome
• Use of corticosteroids or immunosuppressive drugs within 30 days prior to study entry. Participants who have used topical or nasal corticosteroids are not excluded.
• Live vaccine within 4 weeks prior to study entry
• Killed vaccine within 2 weeks prior to study entry
• Blood products within 6 months prior to study entry
• Participation in another investigational vaccine or drug trial within 60 days of starting this study, or while this trial is ongoing
• Previously received a licensed or experimental yellow fever or dengue vaccine
• Surgical removal of spleen
• History of dengue virus infection or other flavivirus infection (e.g., yellow fever virus, St. Louis encephalitis, West Nile virus, Japanese encephalitis virus)
• Other condition that, in the opinion of the investigator, would affect the participant's participation in the study
• Plan to travel to an area where dengue infection is common
• Pregnancy or breastfeeding