Evaluation of Safety and Immunogenicity of the Recombinant ZR202-CoV and ZR202a-CoV Vaccines in Adults.

Inclusion Criteria: 1. Adults of both genders, 18 years of age and older, not older than 55 years of age in Part 1. 2. The subject has a BMI (Body Mass Index) ≤30 kg/m2, inclusive, at Screening. 3. Having understood the contents of the ICF and patient information sheet, and having signed the ICF. 4. Free of obvious health problems as established by medical history including physical examination and clinical judgment of the investigator. 5. Clinical laboratory test results within normal reference range, or results with acceptable deviations that are judged to be NCS (Not Clinically Significant) by the investigator. (Part 1 only) 6. Willing to come to study site and/or to receive home visits for the entire study period. 7. Residence in the study area. 8. Female subjects of childbearing potential have used available contraceptive methods during their sexual life within 14 days before enrollment, have no pregnancy plan and will take effective contraceptive measures from enrollment to 1 month after the 2nd vaccination. Exclusion Criteria: 1. Medical history of COVID-19 or previous vaccination with SARS-CoV-2 vaccine. 2. Fever (body temperature ≥37.5℃/axillary temperature ≥37.3℃) on the day of vaccination or in the 72 hours prior to vaccination. 3. Suffering from any acute clinically significant diseases or being in the acute exacerbation of chronic disease or body temperature ≥37.5℃ (this does not include minor illness such as diarrhea or mild respiratory tract infection) in the 72 hours prior to vaccination. 4. Prior history of allergic reaction or anaphylaxis to any vaccine or drug, e.g., hypersensitivity, urticaria, serious eczema, dyspnea, laryngeal edema, and angioedema etc. 5. Having received or planning to receive any vaccine other than the vaccines used in this clinical study from 28 days prior to the first vaccination to study end (except "vaccines for emergency" such as tetanus vaccine or rabies vaccine). 6. Having participated in or planned to participate in clinical studies of other drugs from 28 days prior to the 1st vaccination to study end (6 months after the 2nd vaccination in Part 1). 7. 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. 8. Having hereditary hemorrhagic tendency or coagulation dysfunction (e.g., cytokine defects, coagulation disorders or platelet disorders), or history of significant bleeding, or history of intramuscular injection or venipuncture injury. 9. Known medical history or a previous diagnosis of thrombosis including thrombocytopenia. 10. Known medical history or diagnosis confirming that subjects have diseases affecting immune system function, including cancer (except skin basal cell carcinoma), congenital or acquired immunodeficiency (e.g., infection with HIV \[Human Immunodeficiency Virus\]), uncontrolled autoimmune disease. 11. Asplenia or functional asplenia. 12. Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying agents within 90 days prior to the administration of study vaccines (including systemic corticosteroids, this means prednisone, or equivalent, ≥0.5 mg/kg/day; topical steroids including inhaled steroids are allowed). 13. Having received immunoglobulins and/or blood products within 3 months prior to the 1st vaccination in this study. 14. Planning to permanently move from the local area before study completion or leave the local area for a long time during the period of study visits. 15. Positive for the pregnancy test (a pregnancy test will be required before each vaccination for all women of childbearing potential) or lactation. 16. Previous inclusion of 5 family members in the study (i.e., subjects belonging to the same family - biological father, mother, child, and brothers and sisters may be included up to a maximum of 5 members from the same family). 17. Any chronic disease, condition, or criteria that in the opinion of the investigator might compromise the wellbeing of the subject or the compliance with study procedures or interfere with the outcome of the study.