Inclusion Criteria:

• A healthy male or female adult 18-45 years at the time of vaccination;
• Free of obvious health problems as established by medical history and physical examination before entering into the study;
• Written informed consent obtained from the subject;
• Able to read the Subject Information Sheet and Consent Form;
• 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) should be enrolled in the study;
• If the subject is female, she must be of non-childbearing potential, i.e. either surgically sterilized or one year post-menopausal; or, if of childbearing potential, she must be abstinent or have used adequate contraceptive precautions (i.e. intrauterine contraceptive device; oral contraceptives or other equivalent hormonal contraception, e.g. progestin implantable, cutaneous hormonal patch or injectable contraceptives) for 30 days prior to vaccination, have a negative pregnancy test within 48 hours prior to vaccination and must agree to continue such precautions for 60 days after completion of the vaccination series.

Exclusion Criteria:

• Pregnant or lactating female;
• Female planning to become pregnant or planning to discontinue abstinence or contraceptive precautions;
• History of any neurological or behavioral disorder or seizures, with the exception of a single febrile seizure in childhood;
• History of drug abuse or alcohol consumption (more than 2 drinks per day);
• History of allergic disease/reaction likely to be exacerbated by any component of the vaccine;
• History of urticaria related to mosquito bites requiring medical attention;
• Acute or chronic, clinically significant pulmonary, cardiovascular, hepatic, renal, hematologic or endocrine functional defect, as determined by physical examination or laboratory tests;
• Any confirmed or suspected immunosuppressive or immunodeficient condition;
• Subject seropositive for HBsAg, anti-HCV or anti-HIV;
• Acute disease at the time of enrollment (acute disease is defined as the presence of a moderate or severe illness with or without fever);
• (Vaccine can be administered to persons with a minor illness such as diarrhea, mild upper respiratory infection with or without low-grade febrile illness, i.e., oral temperature <37.5°C/<99.5°F.)
• Chronic hepatomegaly, right upper quadrant abdominal pain or tenderness;
• Chronic splenomegaly, left upper quadrant abdominal pain or tenderness;
• Use of any investigational or non-registered drug or vaccine other than the study vaccine within 30 days preceding the study vaccine (includes placebo) or planned use during the study period;
• Planned administration of a vaccine not foreseen by the study protocol during the period starting from 30 days before each dose of the study vaccine and ending 30 days after;
• A planned move to a location that will prohibit participating in the trial for 9 months after the initial vaccination;
• Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within 90 days preceding the first dose or planned administration during the study period. For corticosteroids, this will mean prednisone, or equivalent, 0.5 mg/kg/day. Inhaled and topical steroids are allowed;
• Administration of immunoglobulins and/or blood products within 90 days preceding the first dose or planned administration during the study period;
• Any chronic systemic drug therapy to be continued during the study period (except for vitamin/mineral supplements, a single anti-hypertension medication or routine treatment for gastro-esophageal reflux).