To evaluate the immunogenicity and safety of a COVID-19 mRNA vaccine (ZSVG-02-O) in a healthy population aged 18 years and older.

This study uses a randomized, blinded and controlled design, with age stratification of 18-59 years and ≥60 years , including the test vaccine at different doses (30 μg and 60 μg) and an active control vaccine.

A total of 980 subjects will be enrolled in this study. 490 subjects aged 18-59 years will be randomly assigned to cohort A1 (test vaccine dose 1), A2 (test vaccine dose 2) and A3 (control vaccine) for the 2-dose regimen (0,28-day) and to cohort A4 (test vaccine dose 1), A5 (test vaccine dose 2) and A6 (active control) for the 1-dose regimen in a ratio of 3:3:1:3:3:1. Another 490 subjects aged 60 years or older will be randomized to cohort B1 (test vaccine dose 1), B2 (test vaccine dose 2) and B3 (active control) for the 2-dose regimen (0,28-day), and cohort B4 (test vaccine dose 1), B5 (test vaccine dose 2) and B6 (control vaccine) for the 1-dose regimen in a ratio of 3:3:1:3:3:1.

Inclusion Criteria:

1. Healthy male or female subjects aged ≥18 years of age;
2. Subjects who are in good physical condition as judged by the investigator based on medical history, physical examination and clinical laboratory tests;
3. Subjects who have not been previously vaccinated with a Covid-19 vaccine or who have received the last dose (total dose ≤ 3 doses) of a Covid-19 vaccine at least 6 months ago;
4. Subjects who have not been previously infected with Covid-19, or whose nucleic acid or antigen test has turned negative for more than 3 months after previous Covid-19 infection;
5. Subjects are able to understand the study procedures, have provide written informed consent, and are able to comply with the requirements of the clinical study protocol.

Exclusion criteria

1. Axillary temperature ≥37.3°C;
2. Positive polymerase chain reaction (PCR) test results within the last 48 hours;
3. Women of childbearing potential with a positive urine pregnancy test result, or who are pregnant or breastfeeding, or who have not used effective contraception within 2 weeks prior to enrolment, or women and men who plan to have children within 12 months after full immunisation;
4. History of epilepsy, convulsions or seizures, psychosis or family history of psychosis;
5. Have a history of severe allergy to any medication or vaccination (e.g. acute allergic reaction, urticaria, skin eczema, dyspnoea, angioneurotic oedema, or abdominal pain) or allergy to known components of a Covid-19 vaccine;
6. Have a history of hospital-diagnosed thrombocytopenia or other coagulation disorders;
7. Have a history of hospital-diagnosed known immunological impairment or hypofunction;
8. Subjects who have received whole blood, plasma or immunoglobulin therapy within 3 months;
9. Known or suspected concomitant serious diseases, including: respiratory diseases, acute infections or active chronic diseases, liver and kidney diseases, severe diabetes, malignant tumours, infectious or allergic skin diseases, and HIV infection (with test report);
10. Have serious cardiovascular diseases, cardiopulmonary failure, hypertension that cannot be controlled by medication (systolic blood pressure ≥ 140mmHg and/or diastolic blood pressure ≥ 90mmHg on physical examination);
11. Received live attenuated vaccine within 1 month prior to vaccination or other vaccines within 14 days prior to vaccination;
12. Participation in a clinical trial of another drug within 3 months prior to the first dose of vaccine or planning to participate in a clinical trial of another drug during the study period;
13. Any other conditions that the investigator considers inappropriate for participation in this study.