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.