This study is a randomized, double-blinded, and placebo controlled phase III 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 efficacy, safety and immunogenicity of the experimental vaccine in healthy adults aged 18~59 Years.

This study is a randomized, double-blinded, multi-center, placebo-controlled phase III clinical trial in adults aged 18~59 years. The purpose of this study is to evaluate the efficacy, safety and immunogenicity 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 13.000 subjects will be enrolled. Participant will be assigned to receive two doses of experimental vaccine or placebo on the schedule of day 0,14. It is planned that the study will be conducted with two separate cohorts. The first cohort will be healthcare workers in the high risk group (K-1) and the second cohort will be people at normal risk (K-2). After 2 doses of vaccination of 1300 volunteers are completed, safety data will be evaluated by the data safety monitoring board without breaking the blinding, and if there is no safety issue, the K2 cohort will continue to be vaccinated.1.300 volunteers, including 650 volunteers SARS-CoV-2 vaccine and placebo arms, will be included in the K-1 cohort. In the K-2 cohort (normal risk group for COVID-19), 7.650 volunteers were planned to be included in the SARS-CoV-2 vaccine group, and 3.500 volunteers in the placebo group.

Inclusion Criteria:

• 18-59 years of age (including 18 and 59 years of ages),
• For only K1 cohort, health care workers such as medical doctor, nurse, ward boy, cleaner, hospital technician, administrative personnel who work in any department of a hospital.
• Signed informed consent

Exclusion Criteria:

• Previously PCR positive for COVID-19
• IgG or IgM is positive
• For females: Pregnancy (confirmed by positive beta-hCG test), breastfeeding or intent to engage in sexual relations with reproductive intent without use of birth control methods in the three months following vaccination
• Known allergy to components of the study vaccine or control
• Use of immunosuppressant therapy regimens within the six months prior to enrollment in the study or planned use within the two years following enrollment. Immunosuppressant therapy regimens include: antineoplastic chemotherapy, radiation therapy and immunosuppressants to induce transplant tolerance, among others
• Use of immunosuppressive doses of corticosteroids within the three months prior to the enrollment in the study and planned use of immunosuppressive doses of corticoids within the three months following enrollment in the study. Immunosuppressive doses of corticosteroids will be considered the equivalent prednisone 20 mg/day for adults, for longer than one week. Continued use of topical or nasal corticosteroids is not considered an immunosuppressant
• History of asplenia
• History of bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venipuncture
• Any alcohol or drug abuse over the 12 months prior to enrollment in the study that has caused medical, professional or family problems, indicated by clinical history
• Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccine candidate
• Participation in another clinical trial with an investigational product in the six months prior to enrollment in the study or planned participation in another clinical trial within the two years following enrollment
• Received live attenuated virus vaccine 14 days prior to enrollment in the study
• Inactivated vaccine or sub unit vaccine 7 days prior to enrollment in the study
• Fever (oral temperature >37.2℃, axillary temperature will not be accepted) within the past 24 hours
• Any other condition that, in the opinion of the principal investigator or his/her representative physician, could put the safety/rights of potential participants at risk or prevent them from complying with this protocol.
• Any confirmed or suspected autoimmune disease or immunodeficiency disease, including human immunodeficiency virus (HIV) infection.

Double-Blind