1. History of COVID-19, or positive results for either SARS-CoV-2 nucleic acid and antibody tests at screening (outside China only), 2. Suspected or confirmed fever (axillary temperature >= 37.3 degrees/oral temperature >= 37.5 degrees) within 72 hours prior to or on the day of enrollment, 3. History of human coronavirus infection/diseases, such as severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS), 4. Any confirmed or suspected immunosuppression or immunodeficiency status, known history of HIV infection, absence or functional absence of spleen caused by any condition, 5. Presence of severe, uncontrollable or hospitalized cardiovascular diseases, diabetes, neurological diseases (e.g., Green-Barry syndrome), blood and lymphatic diseases, immune diseases, liver and kidney diseases, respiratory diseases (e.g., active tuberculosis, pulmonary fibrosis), metabolic and skeletal diseases, or malignant tumors, 6. Any acute diseases or acute attacks of chronic diseases 3 days prior to enrollment, 7. Genetic predisposition of bleeding, or history of coagulation disorders, thrombotic or bleeding disorders, or conditions that needs continuous anticoagulant usage, 8. History of severe allergy to drugs and vaccines, or to any component of the test vaccine (including the aluminum adjuvant), such as anaphylactic shock, anaphylactic laryngeal edema, anaphylactoid purpura, thrombocytopenic purpura, Arthus reaction, dyspnea, angioneurotic edema, etc., 9. Receipt of any SARS-COV-2 vaccine (including conditional approved/emergency use authorized vaccines or experimental vaccines), 10. Receipt of immunoglobulin and/or other blood products within 3 months prior to vaccination, 11. Receipt of live attenuated vaccine within 28 days prior to vaccination and other vaccines within 14 days prior to vaccination, 12. Previously or currently participation of any other COVID-19 prophylactic drug trials during the study (if subjects underwent hospitalization owning to COVID-19, participation in a treatment trial is permitted, but should notify the investigators immediately), 13. Long-term receipt (> 14 consecutive days) of glucocorticoid (reference value for dose: >= 20 mg/day prednisone or equivalent) or other immunosuppressive agents within the past 6 months, with exception of inhaled or topical corticosteroids, or short-term use (<= 14 consecutive days) of oral corticosteroids, 14. Lactating females, 15. Suspected or known history of severe alcohol (alcoholism) or drug dependence, 16. History or family history of psychiatric illness that may affect trial outcomes, 17. Planned permanent relocation from the study sites during the study or prolonged absence from the local area (affecting the scheduled visit time) during the study visits, 18. Other circumstances which the investigator considers inappropriate for participating in the trial.

1. History of COVID-19, or positive results for either SARS-CoV-2 nucleic acid and antibody tests at screening (outside China only), 2. Suspected or confirmed fever (axillary temperature >= 37.3 degrees/oral temperature >= 37.5 degrees) within 72 hours prior to or on the day of enrollment, 3. History of human coronavirus infection/diseases, such as severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS), 4. Any confirmed or suspected immunosuppression or immunodeficiency status, known history of HIV infection, absence or functional absence of spleen caused by any condition, 5. Presence of severe, uncontrollable or hospitalized cardiovascular diseases, diabetes, neurological diseases (e.g., Green-Barry syndrome), blood and lymphatic diseases, immune diseases, liver and kidney diseases, respiratory diseases (e.g., active tuberculosis, pulmonary fibrosis), metabolic and skeletal diseases, or malignant tumors, 6. Any acute diseases or acute attacks of chronic diseases 3 days prior to enrollment, 7. Genetic predisposition of bleeding, or history of coagulation disorders, thrombotic or bleeding disorders, or conditions that needs continuous anticoagulant usage, 8. History of severe allergy to drugs and vaccines, or to any component of the test vaccine (including the aluminum adjuvant), such as anaphylactic shock, anaphylactic laryngeal edema, anaphylactoid purpura, thrombocytopenic purpura, Arthus reaction, dyspnea, angioneurotic edema, etc., 9. Receipt of any SARS-COV-2 vaccine (including conditional approved/emergency use authorized vaccines or experimental vaccines), 10. Receipt of immunoglobulin and/or other blood products within 3 months prior to vaccination, 11. Receipt of live attenuated vaccine within 28 days prior to vaccination and other vaccines within 14 days prior to vaccination, 12. Previously or currently participation of any other COVID-19 prophylactic drug trials during the study (if subjects underwent hospitalization owning to COVID-19, participation in a treatment trial is permitted, but should notify the investigators immediately), 13. Long-term receipt (> 14 consecutive days) of glucocorticoid (reference value for dose: >= 20 mg/day prednisone or equivalent) or other immunosuppressive agents within the past 6 months, with exception of inhaled or topical corticosteroids, or short-term use (<= 14 consecutive days) of oral corticosteroids, 14. Lactating females, 15. Suspected or known history of severe alcohol (alcoholism) or drug dependence, 16. History or family history of psychiatric illness that may affect trial outcomes, 17. Planned permanent relocation from the study sites during the study or prolonged absence from the local area (affecting the scheduled visit time) during the study visits, 18. Other circumstances which the investigator considers inappropriate for participating in the trial.