This clinical trial is a phase I/II clinical trial to evaluate the safety, immunogenicity and immune persistence of COVID-19 mRNA vaccine in healthy people aged 18 years and above.

This is the clinical trial including an open-label, single-arm Phase I study and a subsequent randomized, blind, placebo-parallel controlled Phase II study to evaluate the safety, immunogenicity and immune persistence of COVID-19 mRNA vaccine in healthy people aged 18-60 years and ≥18 years respectively, whose locations or circumstances put them at appreciable risk of acquiring COVID-19 and/or SARS-CoV-2 infection.

Inclusion Criteria:

• People aged 18-60 years (both inclusive) for phase 1 and aged ≥18 years for phase 2；
• Medical history and physical examination indicating as a healthy person;
• The female participant or the spouse (or partner) of the male participant in child-birthing age agrees to use effective contraceptive measure throughout the whole course of this clinical trial.
• Those who are participating in this clinical trial voluntarily, have signed the informed consent form, and been able to understand and comply with the requirements of the clinical trial protocol.

Exclusion Criteria:

• Confirmed cases or history of SARS-CoV-2 infection;
• Has a history of SARS and MERS virus infection;
• Has fever (axillary temperature ≥37.3℃), dry cough, fatigue, nasal congestion, runny nose, sore throat, myalgia, diarrhea, shortness of breath, and dyspnea within 14 days before vaccination;
• Positive urine pregnancy test；
• Axillary temperature ≥37.3℃ at the day vaccinated;
• History of severe allergic reactions to vaccination (such as acute allergic reactions, urticaria, dyspnea, angioneurosis, edema, etc.) or allergies to known components of COVID-19 mRNA vaccine;
• History or family history of convulsions, epilepsy, encephalopathy, or mental illness;
• Suffering from congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc.;
• Known suffering from diseases including: acute respiratory disease (such as flu-like illness, acute cough, sore throat), severe cardiovascular disease, kidney disease, uncontrolled hypertension (systolic blood pressure >150 mmHg, diastolic blood pressure >90 mmHg), diabetes complications, malignant tumor, all sorts of acute illness or chronic diseases acute phase;
• Diagnosis with congenital or acquired immunodeficiency, HIV infection, lymphoma, leukemia, or other autoimmune disease;
• Abnormal coagulation function (such as lack of coagulation factor, coagulation disorders);
• Receiving anti-tuberculosis treatment;
• Long-term receipt (continuous≥7 days) of glucocorticoid (reverence value for dose: amount to≥20 mg/d prednisone equivalent), except inhaled, topical, nasal, aural and ophthalmic corticosteroids, within 6 months before screening; Receipt of immunotherapy or immunosuppressant within 3 months (continuous oral or infusion for more than 14 days);
• Receipt of live attenuated vaccine within 28 days prior to vaccination and other vaccines within 14 days prior to vaccination;
• Receipt of blood products within 3 months prior to vaccination
• Receipt of other study drugs within 6 months prior to vaccination;
• Receipt of any SARS-COV-2 vaccine;
• Other situations judged by the investigators that are not suitable for participating in this clinical trial.