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 rDEN3delta30/31-7164.

This study will consist of two groups, with Group 1 enrolling first. Group 1 participants will be randomly assigned to receive either 10^3 PFU of rDEN3delta30/31-7164 or placebo subcutaneously in their deltoid. Participants will be monitored at the clinic for 30 minutes after receiving the immunization to monitor for adverse effects. After that, participants will be asked to return to the clinic approximately every other day for the next 16 days, and then on Day 21, 28, 42, and 180. At each visit participants will have physical and clinical exams, vital signs, measures, blood drawn, and will be asked about any adverse events they may have experience. Female participants will be given a pregnancy test. In addition, participants will be asked to measure their temperature 3 times a day and record it in a temperature diary for the first 16 days after immunization.

If less than 90% of the participants in Group 1 seroconvert to DEN3 then Group 2A will be enrolled. Group 2A will follow the same procedures as Group 1, but will receive a 10^5 PFU dose of rDEN3delta30/31-7164.

If more than 90% of the participants in Group 1 seroconvert to DEN3 then Group 2B will be enrolled. Group 2A will follow the same procedures as Group 1, but will receive a 10^1 PFU dose of rDEN3delta30/31-7164.

Inclusion Criteria:

• Adult male or non-pregnant female between 18 and 50 years of age, inclusive.
• Good general health as determined by physical exam, laboratory screening, and review of medical history
• Available for the duration of the study, approximately 26 weeks post-vaccination
• Willing to use effective means of contraception for the duration of the trial

Exclusion Criteria:

• Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, or renal disease by history, physical examination, and/or laboratory studies
• Behavioral, cognitive, or psychiatric disease that in the opinion of the investigator affects the ability of the volunteer to understand and cooperate with the requirements of the study protocol
• Grade 1 or above values for absolute neutrophil count (ANC), alanine aminotransferase (ALT), and serum creatinine, as protocol defined
• Any other condition that in the opinion of the investigator would jeopardize the safety or rights of a volunteer participating n the trial or would render the volunteer unable to comply with the protocol
• Any significant alcohol or drug abuse in the past 12 months which has caused medical, occupational, or family problems, as indicated by volunteer history
• History of a severe allergic reaction or anaphylaxis
• Severe asthma (emergency room visit or hospitalization within the last 6 months)
• Positive HIV-1 serology by screening and confirmatory assays
• Positive for hepatitis C virus (HCV) by screening and confirmatory assays
• Positive for hepatitis B virus (HBV) by hepatitis B surface antigen (HBsAg) screening
• Any known immunodeficiency syndrome
• Use of corticosteroids (excluding topical or nasal) or immunosuppressive drugs within 30 days prior to Study Day 0
• Receipt of a live vaccine within 4 weeks or a killed vaccine within the 2 weeks prior to Study Day 0 or anticipated receipt of any vaccine during the 42 days following Study Day 0
• History of a surgical splenectomy
• Receipt of blood products within the past 6 months, including transfusions or immunoglobulin or anticipated receipt of any blood products or immunoglobulin during the 42 days following Study Day 0
• History or serologic evidence of previous dengue virus infection or other flavivirus infection (e.g., yellow fever virus, St. Louis encephalitis, West Nile virus)
• Previous receipt of yellow fever or dengue vaccine (licensed or experimental)
• Receipt of any investigational agent in the 30 days prior to Vaccination Day 0 or plan to participate in any investigational drug trials during the next 26 weeks
• Definite plans to travel to a dengue endemic area
• Pregnancy or breastfeeding