A Two-dose Primary Vaccination Study of a Tetravalent Dengue Virus Purified Inactivated Vaccine vs. Placebo in Healthy Adults (in Puerto Rico)

Inclusion Criteria: * Subjects who the investigator believes can and will comply with the requirements of the protocol (e.g., completion of the diary cards, return for follow-up visits, etc.) * A male or female between 20 and 39 years of age (inclusive) at the time of consent * Written informed consent obtained from the subject * Healthy subjects as established by medical history and clinical examination before entering into the study * Subject has lived in the Caribbean for more than 10 years * Female subjects of non-childbearing potential (non-childbearing potential is defined as having either a current tubal ligation at least three months prior to enrollment, hysterectomy, ovariectomy, or is post-menopause). * Female subjects of childbearing potential may be enrolled in the study, if the subject has: * practiced adequate contraception for 30 days prior to vaccination, and * a negative urine pregnancy test on the day of vaccination, and * agreed to continue adequate contraception until two months after completion of the vaccination series Exclusion Criteria: * Use of any investigational or non-registered product (drug or vaccine) other than the study vaccines/placebo during the period starting 30 days preceding the first dose of study vaccine/placebo and/or planned use during the study period * Chronic administration (defined as more than 14 days in total) of immunosuppressants or other immune-modifying drugs during the period starting 180 days prior to the first vaccine/placebo dose (for corticosteroids, this will mean prednisone ≥ 20 mg/day or equivalent; inhaled and topical steroids are allowed) * Planned administration or administration of a vaccine/product not foreseen by the study protocol during the Exclusion: * Use of any investigational or non-registered product (drug or vaccine) other than the study vaccines/placebo during the period starting 30 days preceding the first dose of study vaccine/placebo and/or planned use during the study period * Chronic administration (defined as more than 14 days in total) of immunosuppressants or other immune-modifying drugs during the period starting 180 days prior to the first vaccine/placebo dose (for corticosteroids, this will mean prednisone ≥ 20 mg/day or equivalent; inhaled and topical steroids are allowed) * Planned administration or administration of a vaccine/product not foreseen by the study protocol during the period starting 30 days prior to the first dose of vaccine/placebo until after the visit at Day 56 (if influenza activity warrants vaccination of healthy young adults, influenza vaccination will be encouraged and will not lead to study exclusion) * Previous or planned administration of any other flavivirus vaccine (approved or investigational) for the entire study duration * Previous receipt of any investigational dengue virus vaccine * Concurrently participating in another clinical study, at any time during the study period, in which the subject has been or will be exposed to an investigational or a non-investigational product (pharmaceutical product or device). * Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination (no laboratory testing required). * Family history of congenital or hereditary immunodeficiency * History of, or current auto-immune disease * History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine/placebo or related to a study procedure * Major congenital defects or serious chronic illness * History of any neurological disorders or seizures * Acute disease and/or fever (≥37.5°C/99.5°F oral body temperature) at the time of enrollment (a subject with a minor illness, i.e., mild diarrhea, mild upper respiratory infection, etc., without fever, may be enrolled at the discretion of the investigator) * Acute or chronic, clinically significant pulmonary, cardiovascular, hepatic or renal functional abnormality, as determined by physical examination or laboratory screening tests * Administration of immunoglobulins and/or any blood products during the period starting 90 days preceding the first dose of study vaccine/placebo or planned administration during the study period * History of chronic alcohol consumption and/or drug abuse * Pregnant or lactating female or female planning to become pregnant or planning to discontinue contraceptive precautions * A planned move to a location that will prohibit participating in the trial until study end for the participant * Any other condition which, in the opinion of the investigator, prevents the subject from participating in the study. * Subject seropositive for hepatitis B surface antigen (HBsAg), hepatitis C virus antibodies (anti-HCV), or human immunodeficiency virus antibodies (anti-HIV) * Safety laboratory test results that are outside the normal limits for their age, gender, and locality at screening.