A dose escalating study with 3 different dosing regimens of the studied vaccine (JECEVAX- VABIOTECH-Vietnam) and a licensed vaccine (JEVAX-VABIOTECH-Vietnam) is conducted in Vietnamese children, aged 9 to 24 months to assess the safety and immunogenicity. Two hundred children are enrolled and randomly assigned into 4 groups (50 children/group), each of which receive 2 doses of study / control vaccine subcutaneously, at 10-12 days interval. Safety issues included immediate reaction at the site of injection and systemic reaction within 30 min of administration, solicited and unsolicited adverse events occurs from the first dose to 30 days after second dose; SAE (from start of first dose to 30 days after second dose), blood cell count, urea, ALT, AST. Immunogenicity outcomes include seroconversion of neutralizing antibodies (blood samples are taken prior to 1st dose and 20-22 days post 2nd dose).

Mouse brain-derived Japanese Encephalitis (JE) vaccine was developed in Vietnam since 1989 with the support from WHO and BIKEN institute, Japan. It helped Viet Nam prevents Japanese Encephalitis outbreaks successfully during those years.

However, mouse brain-derived JE vaccine production requires companies to compliance various requirements from WHO. Especially, WHO has a plan to replace the mouse brain-derived JE vaccines with Cell culture-derived JE vaccines.

Vero cell-derived vaccine technology shows many advantages compares to Mouse brain-derived vaccine technology. VABIOTECH has been approved and sponsored by the Ministry of Science and Technology to produce Vero cell - derived JE vaccine. The vaccine demonstrated a good safety and immunogenicity profile in animal models. The vaccine has been proven safety in volunteer adults.

In this study, a dose escalating study with 3 different dosing regimens of the studied vaccine (JECEVAX) and a licensed vaccine (JEVAX-VABIOTECH Vietnam) is conducted in Vietnamese children, aged 9-24 months to assess the safety and immunogenicity. Two hundred children are enrolled and randomly assigned into 4 groups (50 children/group), each of which receive 2 doses of investigate vaccines or control vaccine subcutaneously, at 10-12 days interval. Safety issues included immediate reaction at the site of injection and systemic reaction within 30 min of administration, solicited and unsolicited adverse events occurs from the first dose to 30 days after second dose; SAE (from start of first dose to 30 days after second dose), blood cell count, urea, ALT, AST. Immunogenicity outcomes include seroconversion of neutralizing antibodies (blood samples are taken prior to 1st dose and 20-22 days post 2nd dose).

Inclusion Criteria:

• Healthy children of both sexes, 9-24 months of age;
• Have not been vaccinated with JE vaccine;
• Not have any chronic disease;
• Parents/legal guardians agree to participate their children in this study and sign the informed consent.

Exclusion Criteria:

• Currently has chronic diseases (cardiovascular, liver and spleen related etc);
• Currently has acute diseases;
• Use (orally or injection) with corticosteroid containing drug (>1 mg / kg dose);
• Use of immunocompromised treatment within 4 weeks of enrollment;
• Being immunocompromised and autoimmune diseases (HIV, lupus);
• The family history of immunocompromised;
• History of febrile seizure;
• Allergic to any vaccine component;
• Fever (>38 Celsius degree) within 3 days before vaccination or at enrollment;
• Malnourished (3rd grade or above);
• Blood disorder;
• Use of vaccines which have not been licenced 7 days before enrolment in this study

Individual data with identification removed are to be available for Ethical committee, Ministry of Health and National Foundation of Science and Technology Development to avoid misuse of data.

Public shared data will be in the form of summarised tables and figures.