Observer-blind, randomized, active-controlled prospective intervention study

This trial is randomized, prospective intervention study. A total of 4,050 subjects (COVID-19 vaccine naive) who are willing to participate in the study by signing the consent form, will be involved in this trial. The subjects will be divided into three study subsets, namely Main Study I, Main Study II, and Exploratory Study: Main Study I for immunogenicity and safety evaluation, Main Study II for safety evaluation, and Exploratory Study for cellular immunity evaluation, with trial design as follow :

• Main Study I, Exploratory Study subset: Observer-blind, randomized, active-controlled prospective intervention study
• Main Study II: Open-label, randomized study to evaluate safety I

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, 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 in the previous 4 weeks received a treatment likely to alter the immune response (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 active comparator are masking, lot number is masking