A study of the study 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 of the study vaccine compares to licenced vaccine. Two hundred and twenty children are enrolled and randomly assigned into 2 groups (110 children/group), each of which receive 2 doses of study / control vaccine subcutaneously, at 28-34 days interval. Safety data included immediate reaction at the injection site and systemic reaction within 30 min of administration, solicited and unsolicited adverse events occurs from the 1st dose to 28-34 days after first dose and from the second dose to 28-34 days after 2nd dose. SAE (from start of first dose to 28-34 days after second 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 and in phase 2 which evaluated the safety and immunogenicity of 3 difference antigen concentrations.

In this study, a selected dose of the studied vaccine (JECEVAX) derived from phase 2 will be compared the safety with a licensed vaccine (JEVAX-VABIOTECH Vietnam) in Vietnamese children, aged 9-24 months to assess the safety and immunogenicity. Two hundred and twenty children are enrolled and randomly assigned into 2 groups (110 children/group), each of which receive 2 doses of investigate vaccines or control vaccine subcutaneously, at 28-34 days interval. Safety data included immediate reaction at the injection site and systemic reaction within 30 min of administration, solicited and unsolicited adverse events occurs from the 1st dose to 28-34 days after first dose (up to date of 2nd dose) and from the second dose to 28-34 days after 2nd dose (up to date of 3rd visit). SAE (from start of first dose to 28-34 days after second dose - date of 3rd visit).

Inclusion Criteria:

• Healthy children of both sexes, 9-24 months of age;
• Have not been vaccinated with JE vaccine;
• Parents/legally guardians agree their children to participate in the study and sign the paper informed consent.

Exclusion Criteria:

• Currently has chronic diseases (cardiovascular, liver and spleen related etc);
• Currently has acute diseases;
• 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 (2nd 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.