This study is a double-blind, randomized phase Ⅳ clinical trial of the inactivated SARS-CoV-2 vaccine (CoronaVac)manufactured by Sinovac Research & Development Co., Ltd. The purpose of this study is to evaluate the lot-to-lot consistency ,immunogenicity and safety of COVID-19 vaccine between the commercialized scale in workshop 2 and 3 and the commercialized scale in workshop 1 in healthy children aged 3-17 years.

This study is a double-blind, randomized phase Ⅳ clinical trial in healthy children aged 3-17 years to evaluate the lot-to-lot consistency, immunogenicity and safety of the commercial-scale CoronaVac in healthy children aged 3-17 years .The experimental vaccine was manufactured by Sinovac Research & Development Co.,Ltd. A total of 2520 healthy subjects aged 3 to 17 years old will be enrolled.The subjects will be randomly divided into 7 groups of 360 participants per group with an equal probability to received 7 batches of commercial-scale vaccine.All subjects received two doses of vaccine on day 0 and day 28.

Inclusion Criteria:

• Healthy children aged 3-17;
• The subjects and/or guardians can understand and voluntarily sign the informed consent form (For subjects aged 8-17 years, both subjects and guardians need to sign the informed consent form)
• Proven legal identity.

Exclusion Criteria:

• History of SARS-CoV-2 infection;
• History of receiving COVID-19 vaccine;
• 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,absence of spleen, functional absence of spleen, absence of spleen due to any condition or splenectomy;
• 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;
• 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;
• Onset of various acute or chronic diseases within 7 days prior to the study;
• Axillary temperature >37.0°C;
• The subjects participated in other clinical trials during the follow-up period, or will be planned within 3 months;
• Already pregnant (including a positive urine pregnancy test) or are breastfeeding, planning to get pregnant within 2 months;
• According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.