Monitoring JE Antibody Levels in Healthy Populations and Immunization Strategy in Low-Prevalence Areas

This study aims to assess the neutralizing antibody levels and prevalence risk of Japanese encephalitis among residents in low-endemic areas, as well as to evaluate the immunogenicity, safety, and immune persistence of the inactivated Japanese encephalitis vaccine across different age groups in healthy populations. The study uses an open-label, single-arm trial design with a sample size of 250 participants. Primary endpoints include pre- and post-vaccination serum neutralizing antibody levels, seroconversion rates, and incidence of adverse events.

This study aims to gain an in-depth understanding of neutralizing antibody levels against Japanese encephalitis among residents in low-endemic areas to assess potential outbreak risks and to evaluate the immunogenicity, safety, and immune persistence of the inactivated Japanese encephalitis vaccine across different age groups in a healthy population. This open-label, single-arm trial is structured in two phases: Phase I will involve stratified sampling of residents aged 6 years and older for serological testing, followed by administration of the inactivated JE vaccine to assess safety, with serological testing conducted 28 days post-vaccination. Phase II will conduct serological testing 365 days post-primary immunization to evaluate immune persistence.

The target population includes residents aged 6 and older, divided into Group A (ages 6-17), Group B (ages 18-39), and Group C (ages 18+), with different vaccine dosages for each group. Inclusion criteria encompass age, health status, and informed consent, while exclusion criteria cover allergies, serious illness, and recent vaccination. Primary endpoints will include pre- and post-vaccination serum neutralizing antibody levels, seroconversion rates, average antibody levels, and post-vaccination adverse event incidence. The project is scheduled to begin in October 2024 and conclude in December 2026, with the primary research unit being the Liaoning Provincial Center for Disease Control and Prevention, aiming to provide a scientific basis for JE control and prevention in this region.

Eligibility Criteria:
Inclusion Criteria:

* Permanent residents aged 6 years (inclusive) and older;
* Healthy individuals as determined clinically after inquiring about medical history and conducting relevant physical examinations;
* Individuals who meet the vaccination criteria for the inactivated Japanese encephalitis vaccine (Vero cells);
* Participants must provide informed consent to receive vaccination and blood c collection; minors must obtain informed consent from their guardians;
* Participants planned to be included in Group A must have previously completed the full vaccination schedule for the Japanese encephalitis vaccine (including live attenuated vaccine or inactivated vaccine).

Exclusion Criteria:

* Participants are unwilling to sign the informed consent form;
* History of allergy to the vaccine or its components, severe adverse reactions to the vaccine such as allergies, urticaria, breathing difficulties, angioedema, or abdominal pain;
* Individuals with encephalopathy, uncontrolled epilepsy, and other progressive neurological diseases;
* History of seizures or convulsions, or family history of psychiatric disorders;
* Presence of congenital malformations or developmental disorders, genetic defects, and severe malnutrition;
* Individuals with autoimmune diseases, congenital or acquired immunodeficiencies, or family history of autoimmune diseases or immunodeficiencies;
* Any acute diseases or acute exacerbations of chronic diseases in the past 7 days;
* Treatment with immunosuppressants, anti-allergy treatments, cytotoxic therapies, or inhaled corticosteroids (excluding corticosteroid spray treatments for allergic rhinitis or topical corticosteroid treatments for acute non-complicated dermatitis) in the past 6 months;
* Administration of immunoglobulin injections within 1 month prior to vaccination;
* Individuals with fever before vaccination, with axillary temperature \>37.0°C;
* History of Japanese encephalitis;
* Other factors deemed inappropriate for participation in the clinical observational study as determined by the researcher;
* Participants planned for inclusion in Groups B and C must have received the Japanese encephalitis vaccine (including live attenuated vaccine and inactivated vaccine) in the past;
* Pregnant women.