This is a multicenter, randomized, double blind, parallel placebo controlled, phase 3 clinical trial to evaluate the protective efficacy, safety and immunogenicity of inactivated SARS-CoV-2 vaccines in healthy population 18 years old and above.

This is a multicenter, randomized, double-blind, placebo-controlled study to evaluate the protective efficacy, safety and immunogenicity of inactivated SARS-CoV-2 vaccines in healthy population 18 years old and above. The participants were randomized into three groups of investigational vaccine 1, investigational vaccine 2 and placebo in a 1:1:1 ratio.2 doses of the investigational vaccine or placebo are inoculated into the deltoid muscle of the either arm according to the vaccination schedule of D0 & D21 (+7 days).According to the immune durability results in Phase I/II study, and cross-neutralization assay results, a third dose (booster dose) generates a better immune response and is estimated to offer better protection, therefore, a booster dose will be given after 3 months

Inclusion Criteria:

1. Healthy subjects aged 18 years old and above.
2. By asking for medical history and physical examination, the investigator judged that the health condition is well.
3. Female subjects of childbearing age are not nursing or pregnant at the time of enrolment (negative urine pregnancy test) and have no family planning within the first 3 months after enrolment. Effective contraceptive measures have been taken within 2 weeks before inclusion.
4. During the whole follow-up period of the study, be able and willing to complete the whole prescribed study plan.
5. With self-ability to understand the study procedures, the informed consent & voluntarily sign an informed consent form and be able to comply with the requirements of the clinical study protocol.

Exclusion Criteria:

1. Confirmed acute cases of SARS-CoV-2 Infection.
2. Have a history of SARS, MERS infection (self-report, on-site inquiry).
3. Positive urine pregnancy test result.
4. Fever (body temperature > 37.0 ℃), dry cough, fatigue, nasal obstruction, runny nose, pharyngeal pain, myalgia, diarrhea, shortness of breath and dyspnea occurred within 14 days before vaccination.
5. Axillary body temperature > 37.0 ℃ before vaccination.
6. Previous severe allergic reactions to vaccination (such as acute allergic reactions, urticaria, dyspnea, angioneurotic edema or abdominal pain) or allergy to known ingredients of inactivated SARS-CoV-2 vaccine have occurred.
7. Has a history of convulsion, epilepsy, encephalopathy or mental illness or family history.
8. With congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc.
9. With severe liver diseases, severe kidney diseases defined as eGFR less than 60, uncontrollable hypertension (systolic blood pressure >150 mmHg, diastolic blood pressure > 90 mmHg), diabetic complications, malignant tumors, various acute diseases, or acute attack period of chronic diseases.
10. Has been diagnosed with congenital or acquired immune deficiency, HIV infection, lymphoma, leukemia or other autoimmune diseases.
11. With known or suspected diseases include acute respiratory diseases (e.g. influenza like illness, acute cough, sore throat), severe cardiovascular diseases, liver and kidney diseases, and malignant tumors.
12. Has a history of coagulation dysfunction (e.g. Coagulation factor deficiency, coagulation disease).
13. Receiving anti-TB therapy.
14. Patients receiving immunotherapy or inhibitor therapy within 3 months (continuous oral or infusion for more than 14 days).
15. Live attenuated vaccine is inoculated within 1 month before this vaccination, other vaccines are inoculated within 14 days before this vaccination.
16. Received blood products within 3 months before this vaccination
17. Received other research drugs within 6 months before this vaccination.
18. Other circumstances judged by investigators that are not suitable for this clinical trial.