This trial is observer-blind, comparative, randomized, placebo-controlled phase 2 study. The population is healthy subjects aged 18 and above

The phase 2 is dose-ranging study which will recruit 360 subjects to compare two vaccine formulas to placebo (1:1:1), to evaluate the safety and immunogenicity of the vaccine. The subjects will be given 2 doses of investigational product with 28 days interval between doses.

One selected vaccine formula will be evaluated for safety and persistence antibody until 6 months after the last dose.

Inclusion Criteria:

1. Clinically healthy subjects aged 18 years and above.
2. Subjects have been informed properly regarding the study and signed the informed consent form.
3. Subjects will commit to comply with the instructions of the investigator and the schedule of the trial.

Exclusion Criteria:

1. Subjects concomitantly enrolled or scheduled to be enrolled in another trial.
2. History of vaccination with any COVID-19 vaccine.
3. History of COVID-19 within 1 month (for mild-moderate disease) or 3 months (for severe disease) prior to enrollment.
4. Evolving mild, moderate or severe illness, especially infectious disease or fever (body temperature ≥37.5℃, measured with infrared thermometer/thermal gun).
5. Women who are pregnant or planning to become pregnant during the study period (judged by self-report of subjects and urine pregnancy test results).
6. History of uncontrolled asthma, history of allergy to vaccines or vaccine ingredients, and severe adverse reactions to vaccines, such as urticaria, dyspnea, and angioneurotic edema.
7. History of blood disorders contraindicating intramuscular injection.
8. Patients with serious chronic diseases (serious cardiovascular diseases, uncontrolled hypertension and diabetes, liver and kidney diseases, malignant tumors, etc) which according to the investigator might interfere with the assessment of the trial objectives.
9. History of confirmed or suspected immunosuppressive or immunodeficient state, or received in the previous 4 weeks a treatment likely to alter the immuneresponse (intravenous immunoglobulins, blood-derived products or long-term corticosteroid therapy (> 2 weeks)).
10. History of uncontrolled epilepsy or other progressive neurological disorders, such as Guillain-Barre syndrome.
11. Subjects receive any vaccination (other than COVID-19 vaccine) within 1 month before and after IP immunization.
12. Subjects plan to move from the study area before the end of study period.

Vaccine candidate and placebo are masking, lot number is masking