The aim of this study was to document the immunogenicity and safety of a booster dose of IMOJEV administered at least 12 months after the primary dose.

Primary objective:

• To describe the immune response to Japanese Encephalitis (JE) before and 28 days after a booster dose of IMOJEV administered at least 12 months after primary vaccination with IMOJEV.

Exploratory objectives:

• To describe the safety profile of a booster dose of IMOJEV® .

Participants who previously participated in Study JEC12 (NCT01396512) and were primed with IMOJEV received a booster dose of IMOJEV at least 12 months after the primary dose. Participants were assessed for immune response before and on Day 28 after the booster dose and were monitored for safety through Day 28 post-vaccination for non-serious adverse events (AEs) and up to 6 months post-vaccination for serious AEs The duration of each participant's participation in the study was approximately 6 months.

Inclusion Criteria:

• Must have participated in study JEC12 and received 1 dose of IMOJEV at least 12 months before booster vaccination
• Age 2 to 4 years on the day of inclusion
• In good general health at the time of inclusion
• Informed Concent Form signed and dated by parent(s) or another legally acceptable representative(s)
• Subject and parent(s)/legally acceptable representative(s) able to attend all scheduled visits and comply with all study procedures.

Exclusion Criteria:

• Participation at the time of study enrollment (or in the 4 weeks preceding the trial vaccination) or planned participation during the present trial period in another clinical study investigating a vaccine, drug, medical device, or a medical procedure in the 4 weeks preceding the study vaccination
• Known or suspected congenital or acquired immunodeficiency, or receipt of 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 vaccine used in the trial or to a vaccine containing any of the same substances
• Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with trial conduct or completion
• Receipt of immune globulins, blood or blood-derived products in the past 3 months, that might interfere with the assessment of the immune response
• Previous vaccination against flavivirus disease, including JE, with another vaccine, except with IMOJEV® while participating in JEC12
• Administration of any anti-viral within 2 months preceding Visit 1 and up to the 4 weeks following the study vaccination
• Receipt of any vaccine in the 4 weeks preceding the trial vaccination or planned receipt of any vaccine in the 4 weeks following the trial vaccination, except for inactivated influenza vaccination, which may be received at least 2 weeks before the study vaccine
• History of central nervous system disorder or disease, including seizures
• Planned receipt of any JE vaccine during the course of the study
• History of flavivirus infection (confirmed either clinically, serologically or virologically)
• Administration of systemic corticosteroids for more than 2 consecutive weeks within the 4 weeks preceding vaccination
• Thrombocytopenia, contraindicating vaccination
• Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating vaccination
• Febrile illness (temperature ≥38.0°C) or moderate or severe acute illness/infection 3 days before vaccination as well as the day of vaccination, according to Investigator judgment. A prospective subject should not be included in the study until the condition has resolved or the febrile event has subsided
• In an emergency setting or hospitalized involuntarily
• Identified as a natural or adopted child of the Investigator or employee with direct involvement in the proposed study.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org