Immunogenicity, Safety, and Antibody Persistence of Different Immunization Strategies Against Japanese Encephalitis

The main objective of this study is to evaluate the persistence of Japanese encephalitis antibodies in participants at the age of 6, after they have followed different Japanese encephalitis vaccination schedules. Furthermore, the study will assess the immunogenicity and antibody persistence of primary immunization across different Japanese encephalitis vaccination schedules, as well as the immunogenicity following booster immunizations within these schedules. The safety of each vaccine dose will also be evaluated.

This is a randomized, controlled, open-label, non-inferiority study. Healthy children aged 8 months will be invited to participate and randomly allocated to six groups (Group 1 to Group 6) in a 1:1:1:1:1:1 ratio. They will be administered the inactivated Japanese encephalitis vaccine (JEV-I) and/or the live attenuated Japanese encephalitis vaccine (JEV-L) based on the six schedules delineated in the protocol. The primary immunization will be administered to participants at 8 months of age, and a booster dose will be given at 24 months of age. Additionally, participants in Groups 1, 2, and 5 will receive an additional booster dose at the age of 6.

Blood samples (3 mL) will be collected from participants at 8 months, 24 months, and 6 years of age. Samples will be taken before vaccination and 30 days after it for detecting Japanese encephalitis neutralizing antibodies. The titers of these antibodies will be assayed via the 50% plaque reduction neutralization test. Those in groups 3, 4, and 6 who've completed all immunization procedures by 24 months old will have a blood sample taken at 6 years old.

Eligibility Criteria:
Inclusion Criteria:

* Healthy children aged 8 months who are permanent residents of the study area.
* Legal guardians can understand the requirements and processes of the study, provide written informed consent, and comply with all procedures as required by the clinical research protocol.
* Able to receive the full course of Japanese encephalitis vaccinations according to the immunization strategy in the research protocol, including receiving the primary immunization at 8 months of age and the booster immunizations at 24 months of age and 6 years of age.

Exclusion Criteria:

* Unable to finish the full course of primary and booster immunizations at the study area, and unable to fulfill the follow-up visits prescribed in the protocol.
* Non-compliance with the vaccination strategy for each group, as stated in the protocol, regarding Japanese encephalitis vaccines with proper doses and varieties.
* Allergic to any component of the study vaccine or having a history of allergic reactions to any vaccines.
* Having a history of symptoms or signs of neurological diseases or other contraindications for Japanese encephalitis vaccine vaccination.
* Having used immunosuppressants or blood products following birth.
* Receiving other vaccines simultaneously while receiving the Japanese encephalitis vaccine of this project.
* Any conditions that may interfere with the evaluation of the study, as deemed by the researcher.