The aim of the study is to investigate the memory immune response and the yearly persistence of the immunity against Japanese Encephalitis (JE) after vaccination with Japanese Encephalitis Chimeric Virus Vaccine (JE-CV) in participants previously vaccinated with JE-CV vaccine.

Objectives:

• To describe JE immune status before and after JE-CV vaccination in subjects previously vaccinated with JE-CV vaccine
• To describe the immune status before and after JE-CV vaccination in JE-naïve control subjects.
• To describe the safety (in terms of solicited and unsolicited adverse events) of a single dose of JE-CV vaccine up to 6 months after the last vaccination.
• To describe all related serious adverse events (SAEs) and related deaths from 6 months to 5 years after vaccination in JE-CV-primed subjects.

Study participants who are previously immunized with JE-CV vaccine will receive a booster dose of the JE-CV vaccine and will be followed up for 5 years for immunogenicity.

The control (JE-CV naïve) participants will receive either one dose of JE-CV vaccine or one dose of varicella vaccine.

All participants will be monitored for safety for 6 month post-vaccination.

An individual had to fulfill all of the following criteria in order to be eligible for trial enrollment:

All Participants

• Aged 36 to 42 months on the day of inclusion
• Provision of Informed Consent Form signed by at least one parent or other legally acceptable representative
• Participant and parent/legally acceptable representative or guardian able to attend all scheduled visits and to comply with all trial procedures
• In good general health, based on medical history and physical examination

For JE-CV vaccine primed group only

• Participant who was vaccinated with JE-CV in JEC02 trial (NCT00735644)

An individual fulfilling any of the following criteria was excluded from trial enrollment:

All Participants

• Participation in another clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 4 weeks preceding the trial vaccination

• Planned participation in another clinical trial during the Day 0 - Month 6 period and for Group 1 up to 5 years for any flavivirus vaccine trial

• Receipt of any vaccine* in the 4 weeks preceding the trial vaccination, except for pandemic influenza vaccination, which may be received at least 2 weeks before study vaccines

• Planned receipt of any vaccine* in the 4 weeks following the trial vaccination, except for pandemic influenza vaccine. In the event of local or national immunization program with a pandemic influenza vaccine, participants who receive a pandemic influenza vaccine at any time during the trial will not be withdrawn from the trial.

• Planned receipt of any JE vaccine during the course of the trial

• Administration of any anti-viral within 2 months preceding the trial vaccination and up to 4 weeks following the trial vaccination

• Receipt of blood or blood-derived products in the past 3 months, which might interfere with assessment of the immune response

• 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 corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months)

• Seropositivity for human immunodeficiency virus (HIV), hepatitis B, or hepatitis C, as reported by the parent/legally acceptable representative

• History of central nervous system disorder or disease, including seizures and febrile seizures

• 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 or any underlying illness (such as cardiovascular, kidney, liver or hematological disease or development abnormalities) that, in the opinion of the investigator, is at a stage where it might interfere with trial conduct or completion

  • Except in case of national immunization days with oral polio vaccine

For JE-CV primed participants only

• Receipt of any JE vaccine other than JE-CV during JEC02 trial(NCT00735644) and since the end of JEC02 trial

For JE-CV naïve participants only

• Previous vaccination against flavivirus disease including JE
• History of flavivirus infection either based on clinical suspicion or laboratory proven
• Previous vaccination against varicella
• Previous vaccination with JE-CV in JEC02 study
• History of varicella, confirmed either clinically, serologically, or microbiologically
• Known systemic hypersensitivity or anaphylactic/anaphylactoid reaction to neomycin.
• Known history of thrombocytopenia or idiopathic thrombocytopenic purpura

Temporary Contraindications:

A prospective participant was not to be included in the study until the following conditions and/or symptoms had resolved:

1. Receipt of oral or injected antibiotic therapy within 72 hours prior to the first blood draw (for Groups 1 and 2)
2. Febrile illness (temperature ≥38.0°C [≥100.4°F]) or moderate or severe acute illness/infection (according to investigator judgment) on the day of vaccination (for all participants)

The Investigator was to postpone vaccination until the situation/condition resolved. Vaccination could be postponed within the timeframe for vaccination indicated in the protocol trial flowchart.

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

Adverse event data were collected from Day 0 up Day 14 post-vaccination for solicited AEs, up to Day 28 post-vaccination for unsolicited AEs, and up to 5 years post-vaccination for SAEs.