Phase II Clinical Trial of Recombinant SARS-CoV-2 Spike Protein Vaccine (CHO Cell) for the Prevention of COVID-19

Inclusion Criteria: * Healthy individuals aged 18-59 years as well as 60 years and above who can provide legal identification (males and females are both required). * Willing to participate in the study with informed consent prior to screening * Negative in SARS-CoV-2 IgG and IgM test at screening. * Women of childbearing potential must be using effective method of birth control for 14 days prior to the enrollment of the study and must agree to continue such precautions during the study until 30 days after the second dose of the study vaccine/placebo. * Male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 30 days after the second dose of the study vaccine/placebo. Exclusion Criteria: * Confirmed or asymptomatic COVID-19 cases or SARS-CoV-2 infection(had positive in SARS-CoV-2 nucleic acid test or serological test). * Had a history of traveling or residence in domestic area of high pandemic risk, overseas or epidemic areas, or had a history of contact with confirmed, asymptomatic or suspected COVID-19 cases within the past 14 days; * History of SARS; * Received SARS-CoV-2 vaccines for emergency use or approved SARS-CoV-2 vaccines; * Individuals involving a clinical study within 6 months prior to the screening visit; or planning to participate in another clinical study during study period. * Individual's systolic blood pressure ≥ 150mmHg and/or diastolic blood pressure ≥ 100mmHg at screening visit * Axillary temperature \>=37.3℃ prior to vaccination * Individuals in other acute diseases, or in the acute phase of chronic diseases within 3 days prior to the signing of the informed consent form. * Received immunoglobulin and/or blood product 3 months prior to the first vaccination. * Presence of uncontrolled chronic pulmonary, cardiovascular, renal, hepatic, neurologic, hematologic or metabolic (including diabetes mellitus) disorders, which would include the potential subject in a high-risk category for SARS-CoV-2 infection and/or its complications as judged by the investigator. * Individuals with a history of severe allergic reaction (throat swelling, difficult in breath, dyspnea, or shock). * Individuals who have a history of severe adverse reaction associated with a vaccine or severe allergic reaction \[e.g., anaphylaxis to any component of the study vaccines (S protein, Aluminum hydroxide, CpG adjuvant). * Any autoimmune or immunodeficiency disease/condition \[e.g. human immunodeficiency virus (HIV) infection, Systemic lupus erythematosus (SLE)\] * Received immunoglobulin, blood-derived products within 3 months prior to the first study vaccination. * Abnormal coagulation function (such as coagulation factor deficiency, coagulation disease, platelet abnormality) obvious bruises or coagulopathy. * Pregnant women or breastfeeding women. * According to the judgment of the investigator, subject has or had any other symptoms, medical history and other factors that are not suitable for participating in this clinical trial.