Clinical Trial for Batch Consistency of EV71 Vaccine

Inclusion Criteria: * Infants and young children aged 6 to 35 months. * Able to provide legal identification. * The guardian of the subject has the ability to understand and agrees to sign the informed consent form. Exclusion Criteria: * Previous vaccination with the EV71 vaccine. * History of hand, foot, and mouth disease. * History of allergies, asthma, including allergies to vaccines or vaccine components, and severe adverse reactions to vaccines, such as urticaria, difficulty breathing, angioedema, or abdominal pain. * Congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc. * Autoimmune diseases or immune deficiencies/immunosuppression. * Severe neurological disorders (epilepsy, convulsions, or seizures) or mental illness. * History of thyroidectomy, asplenia, functional asplenia, or any condition leading to asplenia or splenectomy. * Blood coagulation abnormalities diagnosed by a physician (such as clotting factor deficiencies, coagulopathies, platelet abnormalities) or evident bruising or bleeding disorders. * Treatment with immunosuppressants, cytotoxic therapy, or inhaled corticosteroids within 6 months prior to enrollment (excluding corticosteroid nasal spray therapy for allergic rhinitis, or topical corticosteroid treatment for acute non-complicated dermatitis). * Receipt of blood products within 3 months prior to vaccination with the trial vaccine. * Receipt of other investigational vaccines within 30 days prior to vaccination with the trial vaccine. * Receipt of live attenuated vaccines within 14 days prior to vaccination with the trial vaccine. * Receipt of subunit or inactivated vaccines within 7 days prior to vaccination with the trial vaccine. * Any acute illness or acute exacerbation of chronic illness within the past 7 days. * Fever before receiving the investigational vaccine, with an axillary temperature \> 37.0°C. * Any other factors that, in the investigator's judgment, make the subject unsuitable for participation in the clinical trial.