Inactivated Bivalent Enterovirus Vaccine (Vero Cell) Phase I/II Clinical Trial

• Healthy participants aged 18-59 years, 6-12 years, and 6-71 months.
• Participants and/or their guardians can understand and voluntarily sign the informed consent form (participants aged 8-12 years require dual signatures from both participants and their guardians).
• Willing and able to comply with all visit schedules, sample collection, vaccine administration, and other trial procedures.
• Provide legal identification of the participants and/or their guardians.

• History of hand, foot, and mouth disease or EV71 vaccination.
• Known severe allergy to the vaccine or vaccine components, such as urticaria, respiratory distress, and angioedema.
• Congenital abnormalities or developmental disorders, genetic defects (such as Down syndrome, thalassemia, or G6PD deficiency), severe malnutrition, etc.
• Based on medical history and physical examination, the presence of severe chronic diseases, severe cardiovascular diseases, uncontrolled hypertension or diabetes, liver or kidney diseases, etc.
• Based on medical history and physical examination, the presence of autoimmune diseases, immunodeficiency diseases, and/or blood diseases (including but not limited to systemic lupus erythematosus, ankylosing spondylitis, thyroidectomy, autoimmune thyroid disease, any form of malignancy, asplenia, functional asplenia).
• Based on medical history and physical examination, abnormal coagulation function (such as coagulation factor deficiency, coagulation disorders, platelet abnormalities) or obvious bruising or bleeding disorders.
• Based on medical history and physical examination, the presence of severe neurological diseases (epilepsy, convulsions, or seizures), mental illness, or corresponding family history.
• Long-term use (more than 14 days) of corticosteroids or other immunosuppressive agents (excluding corticosteroid sprays for allergic rhinitis and surface corticosteroid treatment for acute non-complicated dermatitis) or cytotoxic therapy or planning to receive such treatment during the trial.
• History of long-term alcohol abuse or drug abuse.
• Females who are breastfeeding, pregnant, or planning to become pregnant within 90 days, or females with positive pregnancy test results. Note: male participants whose spouse plans to become pregnant within 90 days are also included.
• Received immunoglobulin and/or other blood products in the past 3 months or planning to receive such treatment during the trial.
• Received other investigational drugs or vaccines within the past 30 days or planning to receive such drugs or vaccines during the trial.
• Vaccinated with attenuated live vaccines within the past 14 days or subunit or inactivated vaccines within the past 7 days.
• Suspected or confirmed fever within 72 hours before vaccination or axillary temperature >37.0℃ on the day of vaccination.
• Clinical laboratory testing shows laboratory abnormalities beyond the reference range and with clinical significance (applicable only to Phase I clinical trials for adults/6-12-year-old children/24-71-month-old children):

A. Complete blood count: white blood cell count, hemoglobin, platelet count.B. Blood biochemistry: alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), creatinine (CR), fasting blood glucose (Glu).C. Urine routine: urine protein (PRO).

• Any acute illness (with or without fever) or exacerbation of chronic illness within the past 7 days.
• According to the investigator's judgment, there are any other factors that make the participant unsuitable for participation in the clinical trial.