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

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 18 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 * 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). See Definition of Terms for adequate contraception. * 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 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) * Planned administration of any flavivirus vaccine for the entire study duration * 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 acceptable values at screening. The following values are not acceptable: * \>110% upper limit of normal (ULN) for alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, creatinine, serum urea nitrogen (SUN) and bilirubin (total and direct) * \<100% lower limit of normal (LLN) or \> 120% ULN for hemoglobin, hematocrit and platelet count * \<75% LLN or \>110% ULN for total white blood cell count (WBC) Note that all screening laboratory results must be either within normal limits (WNL) or no more than Grade l not clinically significant (NCS) (LLN=lower limit of normal; ULN= upper limit of normal, WNL= within normal limits, NCS= not clinically significant)