Immunogenicity And Safety of COVID-19 Vaccine , Inactivated Co -Administration With EV71 Vaccine (Vero Cell)

Inclusion Criteria: * Children aged 3-5 years ; * The subject and/or guardian can understand and voluntarily sign the informed consent form * Proven legal identity; Exclusion Criteria: * History of contact with a SARS-CoV-2 infection (positive in nucleic acid test) within 14 days; * History of multiple system inflammatory syndrome (MIS-C); * History of hand, foot and mouth disease, herpetic angina or EV71 vaccination; * History of asthma, history of allergy to the vaccine or vaccine components,or serious adverse reactions to the vaccine, such as urticaria, dyspnea,and angioedema; * Congenital malformations or developmental disorders, genetic defects,severe malnutrition, etc.; * Autoimmune disease (Systemic lupus erythematosus)or immunodeficiency / immunosuppression(HIV,history after organ transplantation)； * Severe chronic diseases, severe cardiovascular diseases, hypertension and diabetes that cannot be controlled by drugs, liver or kidney diseases,malignant tumors, etc.; * Severe neurological disease (epilepsy, convulsions or convulsions) or mental illness; * Thyroid disease or history of thyroidectomy, asplenia,functional asplenia, asplenia or splenectomy resulting from any condition; * Diagnosed abnormal blood coagulation function (eg, lack of blood coagulation factors, blood coagulopathy,abnormal platelets) or obvious bruising or blood coagulation; * Immunosuppressive therapy, cytotoxic therapy, inhaled corticosteroids (excluding allergic rhinitis corticosteroid spray therapy, acute noncomplicated dermatitis superficial corticosteroid therapy) in the past 6 months; * History of drug abuse; * Receipt of blood products within in the past 3 months; * Receipt of other investigational drugs in the past 30 days; * Receipt of attenuated live vaccines in the past 14 days; * Receipt of inactivated or subunit vaccines in the past 7 days; * Severe neurological disease (epilepsy, convulsions or convulsions) or mental illness; * Axillary temperature \>37.0°C; * The subjects participated in other clinical trials during the follow-up period, or will be planned within 3 months; * According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.