The purpose of this study is to assess the safety, tolerability, immunogenicity, and duration of immunity of one or two doses of ChimeriVax™-JE vaccine separated by 5 or 6 months in adults.

Objectives:

Safety:

• Obtain safety and tolerability data of a single, fixed dose of ChimeriVax™-JE compared with a placebo in adult volunteers (≥ 18 to <55 years) without prior Japanese encephalitis (JE) vaccination.

Immunogenicity:

• Obtain data on the antibody response in adult volunteers following administration of ChimeriVax™-JE
• Assess the durability of the immune response in adult volunteers over 60 months following one or two doses of ChimeriVax™-JE.

Participants will receive ChimeriVax™-JE or diluent on Day 0 and diluent or ChimeriVax™-JE on Day 28. A subset of participants in each group will receive a booster dose of ChimeriVax™-JE at Month 6. Follow-up visits will occur at 12 and 24 months. Eligible participants will then enter the long-term immunogenicity follow-up period with visits at approximately 36, 48, and 60 months after Day 0. No safety data will be collected in the long-term immunogenicity follow-up period.

Inclusion Criteria :

At entry:

• All aspects of the protocol explained and written informed consent obtained from the subject.
• Aged ≥ 18 to < 55 years.
• In good general health, without significant medical history, physical examination findings, or clinically significant abnormal laboratory results.
• Subject must be available for the study duration, including all planned follow-up visits.
• Has the subject agreed to take the following precautions to avoid insect bites for 7 days following vaccination: (a) wear long-sleeved shirts and trousers?; (b) apply N,N-Diethyl-meta-toluamide (DEET)-containing insect repellents?; (c) Sleep in screened enclosures?
• For female subjects of childbearing potential: Negative serum pregnancy tests. An efficacious hormonal (i.e., oral, implantable or injectable) or barrier method of birth control must be used at least 1 month before Screening and Month 6 and at least 1 month after Day 28 and Month 6. These subjects will sign an agreement that birth control will be practised during the specified periods and will specify the method used. Female subjects unable to bear children must have this documented (e.g., tubal ligation or hysterectomy).

For long-term immunogenicity follow-up period:

• Subject received an initial dose of ChimeriVax™-JE, has a baseline (Day 0) sample and at least one post-vaccination evaluable serological specimen for antibody analysis.
• All aspects of the Long-term Immunogenicity Follow-up Period explained and updated written informed consent obtained from the subject.
• In good general health, without significant medical history that may affect the efficacy endpoints or the ability to take blood samples.

Exclusion Criteria :

• A history of vaccination to Japanese encephalitis (JE). Previous vaccination will be determined by history (interview of subject) and/or by reviewing the subject's vaccination card or other official documentation (either a history of or documentation of vaccination fulfils the criterion for exclusion).
• Known or suspected immunodeficiency (e.g., human immunodeficiency virus [HIV] infection, primary immunodeficiency disorder, leukemia, lymphoma), use of immunosuppressive or antineoplastic drugs (corticosteroids > 10 mg prednisone, or equivalent, for more than 14 days in the last three months).
• Clinically significant abnormalities on laboratory assessment.
• Serious adverse reactions characterised by urticaria or angioedema to a prior vaccine.
• Transfusion of blood or treatment with any blood product, including intramuscular or intravenous serum globulin within six months of the Screening Visit or up to Day 56.
• Administration of another vaccine within 30 days preceding the screening visit or up to Day 56 (these subjects will be rescheduled for vaccination at a later date).
• Physical examination indicating any clinically significant medical condition.
• Body temperature >38.1°C (100.6°F) or acute illness within 3 days prior to inoculation (subject may be rescheduled).
• Intention to travel out of the area prior to the study visit on Day 56.
• Seropositive to hepatitis C virus (HCV) or HIV or positive for hepatitis B (HBV) (antigen).
• Lactation or intended pregnancy in female subjects.
• Excessive alcohol consumption, drug abuse, significant psychiatric illness.
• A known or suspected physiological or structural condition that compromises the integrity of the blood-brain barrier (e.g., significant hypertensive cerebrovascular disease, trauma, ischemia, infection, inflammation of the brain).

For long-term immunogenicity follow-up period:

• History of Yellow Fever or out of study JE vaccination or known flavivirus infection since receiving ChimeriVax™-JE vaccination on Day 0 or Day 28 (during double-blind treatment period of the study). Yellow Fever/JE vaccination or flavivirus infection will be determined by history (interview of subject) and/or by reviewing the subject's medical records. Please note subjects who were flavivirus positive at Day 0 will be allowed to enrol on the study.
• Participation in another JE clinical study.

Adverse event data were collected from day of vaccination (Day 0) for up to 6 months post-vaccination.