Immunogenicity and Safety of ChimeriVax™ Japanese Encephalitis Vaccine in Thai Toddlers and Children

Inclusion Criteria: * Provision of consent form signed by at least one parent or another legally acceptable representative, and by at least one independent witness. * Completion of vaccinations according to the national immunization schedule * Subject and parent/legally acceptable representative able to attend all scheduled visits and comply with all trial procedures. * Previous receipt of two doses of a mouse-brain-derived JE vaccine at 12 to 15 months of age according to the national immunization schedule and aged 2 to 5 years on the day of inclusion. * Aged 12 to 24 months on the day of inclusion and have not received any JE vaccine. Exclusion Criteria: * Participation in another clinical trial investigating a vaccine, drug, medical device, or a medical procedure in the 4 weeks preceding the first trial vaccination. * Known or suspected congenital or acquired immunodeficiency, immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months, or long-term systemic corticosteroids therapy. * Known systemic hypersensitivity to any of the vaccine components or history of a life-threatening reaction to the trial vaccine or to a vaccine containing any of the same substances. * Chronic illness, at a stage that could interfere with trial conduct or completion, in the opinion of the Investigator. * Receipt of blood or blood-derived products in the past 3 months, that might interfere with the assessment of the immune response. * Receipt of hepatitis A vaccine. * History of flavivirus infection (confirmed either clinically, serologically or microbiologically). * Administration of any anti-viral within 2 months preceding the screening visit. * History of central nervous system disorder or disease. * Personal or family history of thymic pathology (thymoma), thymectomy, or myasthenia. * Planned participation in another clinical trial during the present trial period. * Receipt of any vaccine in the 4 weeks preceding the first trial vaccination. * Planned receipt of any vaccine in the 4 weeks following any trial vaccination. * Personal human immunodeficiency virus, hepatitis B or hepatitis C seropositivity in the blood sample taken at screening. * Thrombocytopenia, bleeding disorder or anticoagulants in the 3 weeks preceding inclusion contraindicating IM vaccination. * Previous vaccination against flavivirus disease at any time before the trial other than a mouse-brain-derived JE vaccine given in a two-dose regimen at 12 to 15 months of age in accordance with the national immunization schedule. * Febrile illness or any acute illness/infection on the day of vaccination, according to investigator judgment * History of seizures. * Previous vaccination against flavivirus disease.