• Safety, as defined by frequency of vaccine-related adverse events, as classified by both intensity and severity through active and passive surveillance [ Time Frame: Throughout study ] [ Designated as safety issue: Yes ]
  
• Immunogenicity, as determined by anti-DEN3 neutralizing antibody measured on Days 0, 21, 28, 42, and 180 [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  

• Assess the frequency, quantity, and duration of viremia in each dose cohort studied [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  
• Determine the number of vaccinees infected with rDEN3/4delta30(ME) [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  
• Determine cellular targets of vaccine infection, including peripheral blood mononuclear cells (PBMCs) and skin from participants who are willing to undergo skin biopsy [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  
• Compare the infectivity rates, safety, and immunogenicity between dose groups [ Time Frame: At study completion ] [ Designated as safety issue: No ]
  
• Evaluate the immunopathological mechanism of vaccine-associated rash in those volunteers who are willing to undergo skin biopsy [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  

Dengue viruses, which cause dengue fever and dengue shock syndrome, are a major cause of morbidity and mortality in several of the world's tropical and subtropical regions. The rDEN3/4delta30(ME) vaccine is a live attenuated dengue virus vaccine that may be protective against dengue virus serotype 3 (DEN3). The purpose of this study is to evaluate the safety and immunogenicity of the rDEN3/4delta30(ME) vaccine in healthy adults.

This study will last 40 weeks. Participants will be randomly assigned to receive one of three doses of rDEN3/4delta30(ME) or placebo. Participants in Group 1 will receive the middle dose of rDEN3/4delta30(ME) or placebo at study entry. Group 2a will begin enrollment after the immunogenicity review of all participants in Group 1. Participants in Group 2a will receive the highest dose of rDEN4delta30(ME) or placebo at study entry. Group 2b will begin enrollment after the immunogenicity review of all participants in Group 2a. Participants in Group 2b will receive the lowest dose of rDEN4delta30(ME) or placebo.

After vaccination, participants in all groups will be followed closely every other day for the first 16 days of the study. Participants will take their temperature three times a day through Day 16 and record each measurement in a diary. After Day 16, participants will have study visits on Days 21, 28, 42, and 180; a physical exam and blood collection will occur at all visits. Some participants may be asked to join a skin biopsy substudy.

Inclusion Criteria:

• Good general health
• Available for the duration of the study
• Willing to use acceptable forms of contraception for the duration of the study

Exclusion Criteria:

• Significant neurologic, heart, lung, liver, rheumatologic, autoimmune, or kidney disease
• Behavioral, cognitive, or psychiatric disease that, in the opinion of the investigator, may interfere with the study
• Significant laboratory abnormalities
• Medical, work, or family problems as a result of alcohol or illegal drug use 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 (HCV) infected
• Hepatitis B surface antigen positive
• Immunodeficiency syndrome
• Use of corticosteroids or immunosuppressive medications within 30 days prior to study entry. Participants using 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
• Absence of spleen
• Blood products within 6 months prior to study entry
• Previous dengue virus or other flavivirus (e.g., yellow fever virus, St. Louis encephalitis, West Nile virus) infection
• Previously received yellow fever or dengue vaccine
• Plans to travel to an area where dengue infection is common
• Received an investigational agent within 30 days prior to study entry
• Other condition that, in the opinion of the investigator, would interfere with the study
• Pregnancy or breastfeeding