Overview

This study is a randomized, blinded study to evaluate the lot-to-lot consistency of immunogenicity, safety, and immune persistence of three consecutive manufacturing lots of EV71 vaccine, in 1500 children aged 6-35 months. The primary immunogenicity endpoint is the anti-EV71 neutralizing antibody geometric mean titer (GMT) 30 days after the final dose. The secondary immunogenicity endpoints are the geometric mean fold increases and seroconversion rates of anti-EV71 neutralizing antibodies 30 days after the final dose. The immune persistence endpoints are the seropositive rates as well as GMT of anti-EV71 neutralizing antibodies 12 and 24 months after the final dose. The safety endpoints are the number of adverse events/reactions within 30 minutes after each dose, the number of solicited adverse events/reactions within 7 days after each dose, the number of unsolicited adverse events/reactions within 30 days after each dose, and the number of serious adverse events (SAE) from the first dose to 6 months post the final dose.

Eligibility

Inclusion Criteria:

• Age Requirement: Children aged 6 to 35 months at the time of enrollment.
• Provision of legal Identification: Volunteers and their legal guardians or appointed representatives must provide valid legal identification documents.
• Informed Consent: Legal guardians or appointed representatives of volunteers must have the capacity to understand the informed consent document and the research process, voluntarily participate, sign the informed consent form, and be able to comply with the study's requirements and complete relevant visits on time.
• Temperature Requirement: Axillary body temperature prior to vaccination is less than 37.3°C.

Exclusion Criteria:

        [First Dose Exclusion Criterions] Subjects meeting any of the following exclusion criteria
        will not be eligible for enrollment
          -  Allergic History: Subjects have a previous history of allergies to any component of
             the vaccine (e.g., aluminum hydroxide, glycine), or previous or suspected allergy to
             any vaccine or other serious adverse reaction (e.g., anaphylactic shock, laryngeal
             edema, anaphylactic purpura, thrombocytopenic purpura, local anaphylactic necrosis
             reaction, dyspnea, angioedema, systemic rash and/or urticaria, etc.).
          -  Vaccination History: Subjects received any inactivated vaccine or subunit vaccine
             within 7 days prior to the first dose of the investigational vaccine or any live
             attenuated vaccine within 14 days prior to the first dose of the investigational
             vaccine.
          -  Neurological and Mental Health: Subjects with a history or family history of
             convulsion, epilepsy, encephalopathy, and psychosis.
          -  Health Conditions: Subjects with known severe congenital malformation or developmental
             disorder (e.g., Down syndrome, sickle cell anemia, congenital neurological disorders).
          -  Acute Illness: Subjects have experienced acute illness (e.g., fever) or acute onset of
             chronic illness within 3 days before the first dose of investigational vaccine, or use
             of antipyretic, analgesic, or antiallergic drugs within 3 days before the first dose
             of the investigational vaccine.
          -  Coagulation Abnormalities: Subjects with genetic bleeding tendency, coagulopathy, or a
             history of bleeding disorders.
          -  Organ Removal History: Subjects have a history of surgical removal of the spleen or
             other vital immune organs for any reason.
          -  Blood Conditions: Subjects with blood loss (≥400mL) or receipt of blood transfusion,
             immune globulin (other than hepatitis B immune globulin), or blood products within 3
             months prior to the first dose of the investigational vaccine.
          -  Drug Administration: Subjects use any investigational or unregistered product (drug,
             biological product, or device) within 3 months prior to the first dose of the
             investigational vaccine, or planned use during the study, except the investigational
             vaccine.
          -  Immune Therapy: Subjects have a treatment with immunosuppressive agents within 6
             months before the first dose of the investigational vaccine, such as long-term
             treatment with systemic glucocorticoids (e.g., prednisone or a similar agent for more
             than 2 consecutive weeks within 6 months), but topical use (e.g., ointments, eye
             drops, inhalers, or nasal sprays) would be allowed.
          -  Previous history of receipt of other EV71 vaccines.
          -  Previous history of hand-foot-mouth disease.
          -  Immune-related Disease: Subjects have been diagnosed with an infectious disease that
             may interfere with the conduct or completion of the study (e.g., tuberculosis, viral
             hepatitis, human immunodeficiency virus infection, etc.).
          -  Investigators' Discretion: The final exclusion criterion is the investigator's
             discretion to determine whether a subject is suitable for participation in the study.
        [Contraindication of the second dose of vaccine] Subjects meeting any of the following
        exclusion criteria will not be eligible for the second dose of the investigational vaccine
          -  Meeting allergic conditions that are mentioned in the First Dose Exclusion Criteria
             after the first dose.
          -  Severe Adverse Reactions: Subjects experienced serious adverse reactions after
             receiving the previous vaccine dose.
          -  Other Exclusion Reasons as Determined by the Investigator: The investigator determines
             other reasons for exclusion.