A Clinical Trial of Quadrivalent Influenza Vaccine in Children Aged 3-8 Years Old

vaccine-unprimed children Inclusion Criteria: * Healthy children aged 3-8 years; * The subjects' guardians can understand and voluntarily sign the informed consent form; * Proven legal identity. Exclusion Criteria: * Received any circulating seasonal influenza vaccine prior to enrollment or had an influenza vaccine schedule during the study; * Suffering from seasonal influenza in the past 6 moths; * 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 or immunodeficiency / immunosuppression; * 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 inactivated or subunit vaccines in the past 7 days; * Acute diseases or acute exacerbation of chronic diseases in the past 7 days; * Axillary temperature \>37.0°C; * According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial. vaccine-primed children Inclusion Criteria: * Healthy children aged 3-8 years; * The subjects' guardians can understand and voluntarily sign the informed consent form; * Proven legal identity; * Received at least 1 dose of seasonal influenza vaccine in previous epidemic seasons Exclusion Criteria: * Received an seasonal influenza vaccine for the current epidemic season (2020-2021 epidemic season) prior to enrollment, or had an influenza vaccine schedule during the study; * Suffering from seasonal influenza in the past 6 moths; * 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 or immunodeficiency / immunosuppression; * 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; * Acute diseases or acute exacerbation of chronic diseases in the past 7 days; * Axillary temperature \>37.0°C; * According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.