This study is a randomized, double-blinded, and placebo controlled phase Ⅰ/Ⅱ clinical trial of the SARS-CoV-2 inactivated vaccine manufactured by Sinovac Research & Development Co., Ltd. The purpose of this study is to evaluate the safety and immunogenicity of the experimental vaccine in healthy adults aged 18~59 Years.

This study is a randomized, double-blinded, single-center, placebo-controlled phase Ⅰ/Ⅱ clinical trial in adults aged 18~59 years. The purpose of this study is to evaluate the immunogenicity and safety of the experimental SARS-CoV-2 inactivated vaccine. The experimental vaccine and placebo were both manufactured by Sinovac Research & Development Co., Ltd. A total of 744 subjects will be enrolled, with 144 at phase Ⅰ, and 600 at phase Ⅱ. All of participants in phase Ⅰ will be assigned to receive two doses of experimental vaccine or placebo on the schedule of day 0,14 or day 0,28.300 participants in phase Ⅱ will be assigned to receive two doses of experimental vaccine or placebo on the schedule of day 0,14 or day 0,28 and one dose of booster immunization will be given 6 months after primary immunization of day 0,14 or day 0,28.The other 300 participants in phase Ⅱ will be assigned to receive three doses of experimental vaccine or placebo on the schedule of day 0,14,42 or 0,28,56 .

Inclusion Criteria:

• Healthy adults aged 18-59 years;
• Proven legal identity;
• Participants should be capable of understanding the informed consent form, and such form should be signed prior to enrolment ;

Exclusion Criteria:

• Travel history / residence history of Wuhan city and surrounding areas, or other communities with case reports within 14 days;
• History of contact with a SARS-CoV-2 infection (positive in nucleic acid test) within 14 days;
• Have contacted patients with fever or respiratory symptoms from Wuhan and surrounding areas, or from communities with case reports within 14 days;
• Have contacted patients with fever or respiratory symptoms from Wuhan and surrounding areas, or from communities with case reports within 14 days;
• Self-reported history of SARS;
• Self-reported history of new coronavirus infection;
• Positive in serum antibodies (IgG or IgM) screening of COVID-19;
• Positive in nasopharyngeal swabs or anal swabs through RT-PCR;
• Women who are breastfeeding, pregnant or planning to become pregnant during the study period;
• BMI≥35 kg/m2;
• 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;
• Suffering from severe chronic diseases, severe cardiovascular diseases, hypertension and diabetes that cannot be controlled by drugs, liver and kidney diseases, malignant tumors, etc.;
• Severe neurological disease (epilepsy, convulsions or convulsions) or mental illness;
• Thyroid disease or history of thyroidectomy, spleenlessness, functional spleenlessness, spleenlessness 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 non-complicated dermatitis superficial corticosteroid therapy) in the past 6 months;
• Abnormal laboratory test results in the physical examination such as clinically significant abnormal hematology and biochemistry beyond the reference value range (only applicable to Phase I clinical trials);
• History of alcohol or 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;
• Attacks of acute diseases or 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.