Subjects who meet any of the following criteria will be excluded: 1. Confirmed or asymptomatic COVID-19 cases, 2. Positive SARS-CoV-2 nucleic acid test, 3. Positive SARS-CoV-2 IgG or IgM test (reference to nucleic acid test and chest CT if necessary), 4. History of SARS, 5. Fever (axillary temperature >= 37.3 degrees C) or other acute diseases, or in the acute phase of chronic diseases within 14 days prior to the signing of the informed consent form, 6. With significantly abnormal laboratory test results during screening, including biochemical profile, hematology, urinalysis, coagulation function and antinuclear antibody, 7. Past history of allergies to vaccines (e.g., acute allergic reactions, hives, skin eczema, dyspnea, angioneurotic edema, or abdominal pain), or allergic to any known ingredients of COVID-19 vaccines, 8. History of drug abuse/dependence within 1 year prior to signing the informed consent, 9. Past history of alcoholism, 10. Having severe chronic diseases that cannot be controlled by drugs (individuals >= 60 years): chronic respiratory diseases (including moderate to severe asthma, COPD, pulmonary fibrosis), uncontrolled hypertension (systolic blood pressure >=140 mmHg and/or diastolic blood pressure >= 90 mmHg), severe cardiovascular diseases (including cardiac failure, coronary artery disease, cardiomyopathy), chronic kidney disease, cancer, diabetes (unacceptable glycemia control or serious diabetic complications), 11. History of congenital or acquired angioneurotic edema, 12. Any confirmed or suspected immunosuppressive or immunodeficiency disorder, including HIV infection and asplenia, recurrent severe infections and administration of immunosuppressive drugs during the past 6 months, excluding topical steroids or short-term oral steroids (< 14 days), 13. History of autoimmune diseases, excluding mild psoriasis, controllable autoimmune thyroid disease, vitiligo, or stable celiac disease that does not require immunosuppressive or immunomodulatory therapy, 14. Pregnant women or women expected to get pregnant within 12 months after the last dose and breastfeeding women, 15. At high risk of SARS-CoV-2 exposure (such as medical staff, health care providers in direct contact with patients), 16. Having received SARS-CoV-2 vaccines for emergency use or approved SARS-CoV-2 vaccines, 17. Positive screening test results (Hepatitis C virus antibody, treponema pallidum antibody, HIV antibody), 18. Administration of a live attenuated vaccine within 1 month prior to the investigational vaccine dose, or other vaccines within 14 days prior to the investigational vaccine dose, 19. Administration of immunoglobulins and/or any blood products within 3 months prior to the investigational vaccine dose, 20. Administration of other investigational drugs within 6 months prior to the investigational vaccine dose, 21. Other scenarios that may be medically, psychologically or socially contradicted with the study protocol at the investigators discretion or preclude informed consents of the subjects.

Subjects who meet any of the following criteria will be excluded: 1. Confirmed or asymptomatic COVID-19 cases, 2. Positive SARS-CoV-2 nucleic acid test, 3. Positive SARS-CoV-2 IgG or IgM test (reference to nucleic acid test and chest CT if necessary), 4. History of SARS, 5. Fever (axillary temperature >= 37.3 degrees C) or other acute diseases, or in the acute phase of chronic diseases within 14 days prior to the signing of the informed consent form, 6. With significantly abnormal laboratory test results during screening, including biochemical profile, hematology, urinalysis, coagulation function and antinuclear antibody, 7. Past history of allergies to vaccines (e.g., acute allergic reactions, hives, skin eczema, dyspnea, angioneurotic edema, or abdominal pain), or allergic to any known ingredients of COVID-19 vaccines, 8. History of drug abuse/dependence within 1 year prior to signing the informed consent, 9. Past history of alcoholism, 10. Having severe chronic diseases that cannot be controlled by drugs (individuals >= 60 years): chronic respiratory diseases (including moderate to severe asthma, COPD, pulmonary fibrosis), uncontrolled hypertension (systolic blood pressure >=140 mmHg and/or diastolic blood pressure >= 90 mmHg), severe cardiovascular diseases (including cardiac failure, coronary artery disease, cardiomyopathy), chronic kidney disease, cancer, diabetes (unacceptable glycemia control or serious diabetic complications), 11. History of congenital or acquired angioneurotic edema, 12. Any confirmed or suspected immunosuppressive or immunodeficiency disorder, including HIV infection and asplenia, recurrent severe infections and administration of immunosuppressive drugs during the past 6 months, excluding topical steroids or short-term oral steroids (< 14 days), 13. History of autoimmune diseases, excluding mild psoriasis, controllable autoimmune thyroid disease, vitiligo, or stable celiac disease that does not require immunosuppressive or immunomodulatory therapy, 14. Pregnant women or women expected to get pregnant within 12 months after the last dose and breastfeeding women, 15. At high risk of SARS-CoV-2 exposure (such as medical staff, health care providers in direct contact with patients), 16. Having received SARS-CoV-2 vaccines for emergency use or approved SARS-CoV-2 vaccines, 17. Positive screening test results (Hepatitis C virus antibody, treponema pallidum antibody, HIV antibody), 18. Administration of a live attenuated vaccine within 1 month prior to the investigational vaccine dose, or other vaccines within 14 days prior to the investigational vaccine dose, 19. Administration of immunoglobulins and/or any blood products within 3 months prior to the investigational vaccine dose, 20. Administration of other investigational drugs within 6 months prior to the investigational vaccine dose, 21. Other scenarios that may be medically, psychologically or socially contradicted with the study protocol at the investigators discretion or preclude informed consents of the subjects.

Subjects who meet any of the following criteria will be excluded: 1) Confirmed or asymptomatic COVID-19 cases, 2) Positive SARS-CoV-2 nucleic acid test, 3) Positive SARS-CoV-2 IgG or IgM test (reference to nucleic acid test and chest CT if necessary), 4) History of SARS, 5) Fever (axillary temperature = 37.3?) or other acute diseases, or in the acute phase of chronic diseases within 14 days prior to the signing of the informed consent form, 6) With significantly abnormal laboratory test results during screening, including biochemical profile, hematology, urinalysis, coagulation function and antinuclear antibody, 7) Past history of allergies to vaccines (e.g., acute allergic reactions, hives, skin eczema, dyspnea, angioneurotic edema, or abdominal pain), or allergic to any known ingredients of COVID-19 vaccines, 8) History of drug abuse/dependence within 1 year prior to signing the informed consent, 9) Past history of alcoholism, 10) Having severe chronic diseases that cannot be controlled by drugs (individuals = 60 years): chronic respiratory diseases (including moderate to severe asthma, COPD, pulmonary fibrosis), uncontrolled hypertension (systolic blood pressure >=140 mmHg and/or diastolic blood pressure >=90 mmHg), severe cardiovascular diseases (including cardiac failure, coronary artery disease, cardiomyopathy), chronic kidney disease, cancer, diabetes (unacceptable glycemia control or serious diabetic complications), 11) History of congenital or acquired angioneurotic edema, 12) Any confirmed or suspected immunosuppressive or immunodeficiency disorder, including HIV infection and asplenia, recurrent severe infections and administration of immunosuppressive drugs during the past 6 months, excluding topical steroids or short-term oral steroids (<14 days), 13) History of autoimmune diseases, excluding mild psoriasis, controllable autoimmune thyroid disease, vitiligo, or stable celiac disease that does not require immunosuppressive or immunomodulatory therapy, 14) Pregnant women or women expected to get pregnant within 12 months after the last dose and breastfeeding women, 15) At high risk of SARS-CoV-2 exposure (such as medical staff, health care providers in direct contact with patients), 16) Having received SARS-CoV-2 vaccines for emergency use or approved SARS-CoV-2 vaccines, 17) Positive screening test results (Hepatitis C virus antibody, treponema pallidum antibody, HIV antibody), 18) Administration of a live attenuated vaccine within 1 month prior to the investigational vaccine dose, or other vaccines within 14 days prior to the investigational vaccine dose, 19) Administration of immunoglobulins and/or any blood products within 3 months prior to the investigational vaccine dose, 20) Administration of other investigational drugs within 6 months prior to the investigational vaccine dose, 21) Other scenarios that may be medically, psychologically or socially contradicted with the study protocol at the investigators discretion or preclude informed consents of the subjects.

Subjects who meet any of the following criteria will be excluded: 1) Confirmed or asymptomatic COVID-19 cases, 2) Positive SARS-CoV-2 nucleic acid test, 3) Positive SARS-CoV-2 IgG or IgM test (reference to nucleic acid test and chest CT if necessary), 4) History of SARS, 5) Fever (axillary temperature = 37.3?) or other acute diseases, or in the acute phase of chronic diseases within 14 days prior to the signing of the informed consent form, 6) With significantly abnormal laboratory test results during screening, including biochemical profile, hematology, urinalysis, coagulation function and antinuclear antibody, 7) Past history of allergies to vaccines (e.g., acute allergic reactions, hives, skin eczema, dyspnea, angioneurotic edema, or abdominal pain), or allergic to any known ingredients of COVID-19 vaccines, 8) History of drug abuse/dependence within 1 year prior to signing the informed consent, 9) Past history of alcoholism, 10) Having severe chronic diseases that cannot be controlled by drugs (individuals = 60 years): chronic respiratory diseases (including moderate to severe asthma, COPD, pulmonary fibrosis), uncontrolled hypertension (systolic blood pressure >=140 mmHg and/or diastolic blood pressure >=90 mmHg), severe cardiovascular diseases (including cardiac failure, coronary artery disease, cardiomyopathy), chronic kidney disease, cancer, diabetes (unacceptable glycemia control or serious diabetic complications), 11) History of congenital or acquired angioneurotic edema, 12) Any confirmed or suspected immunosuppressive or immunodeficiency disorder, including HIV infection and asplenia, recurrent severe infections and administration of immunosuppressive drugs during the past 6 months, excluding topical steroids or short-term oral steroids (<14 days), 13) History of autoimmune diseases, excluding mild psoriasis, controllable autoimmune thyroid disease, vitiligo, or stable celiac disease that does not require immunosuppressive or immunomodulatory therapy, 14) Pregnant women or women expected to get pregnant within 12 months after the last dose and breastfeeding women, 15) At high risk of SARS-CoV-2 exposure (such as medical staff, health care providers in direct contact with patients), 16) Having received SARS-CoV-2 vaccines for emergency use or approved SARS-CoV-2 vaccines, 17) Positive screening test results (Hepatitis C virus antibody, treponema pallidum antibody, HIV antibody), 18) Administration of a live attenuated vaccine within 1 month prior to the investigational vaccine dose, or other vaccines within 14 days prior to the investigational vaccine dose, 19) Administration of immunoglobulins and/or any blood products within 3 months prior to the investigational vaccine dose, 20) Administration of other investigational drugs within 6 months prior to the investigational vaccine dose, 21) Other scenarios that may be medically, psychologically or socially contradicted with the study protocol at the investigators discretion or preclude informed consents of the subjects.