Study on the Long-Term Persistence of Immunity Induced by Inactivated Hepatitis A Vaccine

This study is a single-center, open-label, controlled study. Its primary objective is to evaluate the 20-year persistence of immunity induced by the inactivated hepatitis A vaccine. At least 106 healthy participants aged 21-28 years will be enrolled. Participants will be selected from individuals who completed the full vaccination course in the PRO-HA-4006 clinical study (Three-Batch Consistency Study of Healive® in Healthy Children Aged 1-8 Years in Changzhou) . After voluntarily providing informed consent, each participant will undergo one venous blood collection of approximately 3.0 mL for hepatitis A antibody testing to assess the persistence of immunity induced by the hepatitis A vaccine.

Inclusion Criteria: Participants must meet all of the following criteria to be eligible for this study: 1. Healthy participants aged 21-28 years who previously participated in PRO-HA-4006 and completed the full vaccination course; 2. Participants who are able to understand and voluntarily sign the informed consent form; 3. Provision of valid legal identification. Exclusion Criteria: Individuals meeting any of the following criteria will be excluded from this study: 1. History of hepatitis A virus infection; 2. Receipt of any vaccine containing hepatitis A antigen since participation in the PRO-HA-4006 clinical study; 3. Autoimmune disease or immunodeficiency/immunosuppression; 4. Coagulation abnormalities, such as coagulation factor deficiency or platelet abnormalities, or a history of significant bleeding, hematoma, or ecchymosis following intramuscular injection or venipuncture; 5. In the investigator's judgment, any other factor that makes the participant unsuitable for participation in the clinical study.