phase i: a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; presence of fever within 3 days before the study vaccination; a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; previously or currently suffering from clinically significant cardiovascular diseases, or clinically significant disorders related to respiratory system, liver and kidney, gastrointestinal system, endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies, that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other investigational drugs within 1 month before the study vaccination; participants who is at the acute state of disease, such as acute onset of chronic heart failure, acute sore throat, hypertensive encephalopathy, acute pneumonia, acute renal insufficiency, acute cholecystitis; participants received other drug used for prevention of covid-19 (exception for previous mrna vaccine the participant received) ; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology. phase ii: a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; presence of fever within 3 days before the study vaccination; a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix) , such as severe heart failure, severe pulmonary heart disease, unstable angina, liver failure, or uremia; contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other investigational drugs within 1 month before the study vaccination; participants who is at the acute state of disease, such as acute onset of chronic heart failure, acute sore throat, hypertensive encephalopathy, acute pneumonia, acute renal insufficiency, acute cholecystitis; participants received other drug used for prevention of covid-19 (exception for previous mrna vaccine the participant received) ; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; those who are tested positive for hiv in terms of serology.

phase i: a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; presence of fever within 3 days before the study vaccination; a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; previously or currently suffering from clinically significant cardiovascular diseases, or clinically significant disorders related to respiratory system, liver and kidney, gastrointestinal system, endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies, that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other investigational drugs within 1 month before the study vaccination; participants who is at the acute state of disease, such as acute onset of chronic heart failure, acute sore throat, hypertensive encephalopathy, acute pneumonia, acute renal insufficiency, acute cholecystitis; participants received other drug used for prevention of covid-19 (exception for previous mrna vaccine the participant received) ; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology. phase ii: a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; presence of fever within 3 days before the study vaccination; a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix) , such as severe heart failure, severe pulmonary heart disease, unstable angina, liver failure, or uremia; contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other investigational drugs within 1 month before the study vaccination; participants who is at the acute state of disease, such as acute onset of chronic heart failure, acute sore throat, hypertensive encephalopathy, acute pneumonia, acute renal insufficiency, acute cholecystitis; participants received other drug used for prevention of covid-19 (exception for previous mrna vaccine the participant received) ; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; those who are tested positive for hiv in terms of serology.

a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; phase i participants only: high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; presence of fever within or 72 h before the study vaccination (axillary temperature ≥ 37.3℃); a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; phase i participants only: previously or currently suffering from clinically significant cardiovascular diseases (except for the hypertension that can be controlled with drugs), or clinically significant disorders related to respiratory system, liver and kidney (except for light fatty liver), gastrointestinal system (except for chronic gastritis), endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix), that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; phase ii participants only: presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix); contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other investigational drugs within 1 month before the study vaccination; participants who is at the active state of disease; participants received other drug used for prevention of covid-19 (exception for previous adenovirus vectored or mrna vaccine the participant received) ; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; phase i participants only: those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology; phase ii participants only: those who are tested positive for hiv in terms of serology.

a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; phase i participants only: high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; presence of fever within or 72 h before the study vaccination (axillary temperature ≥ 37.3℃); a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; phase i participants only: previously or currently suffering from clinically significant cardiovascular diseases (except for the hypertension that can be controlled with drugs), or clinically significant disorders related to respiratory system, liver and kidney (except for light fatty liver), gastrointestinal system (except for chronic gastritis), endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix), that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; phase ii participants only: presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix); contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other investigational drugs within 1 month before the study vaccination; participants who is at the active state of disease; participants received other drug used for prevention of covid-19 (exception for previous adenovirus vectored or mrna vaccine the participant received) ; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; phase i participants only: those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology; phase ii participants only: those who are tested positive for hiv in terms of serology.

a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; phase i participants only: high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; presence of fever within or 72 h before the study vaccination (axillary temperature ≥ 37.3℃); a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; phase i participants only: previously or currently suffering from clinically significant cardiovascular diseases (except for the hypertension that can be controlled with drugs), or clinically significant disorders related to respiratory system, liver and kidney (except for light fatty liver), gastrointestinal system (except for chronic gastritis), endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix), that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; phase ii/iii participants only: presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix); contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other registered investigational drugs of intervention within 1 month before the study vaccination; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding or plan to be pregnant during the study period; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; phase i participants only: those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology; phase ii/iii participants only: those who are tested positive for hiv in terms of serology.

a participant who conforms to any of the following criteria should not be enrolled in the study: previous diagnosis of covid-19; phase i participants only: high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; presence of fever within or 72 h before the study vaccination (axillary temperature ≥ 37.3℃); a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; a medical or family history of seizure, epilepsy, encephalopathy and psychosis; immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. patients on antituberculosis therapy; phase i participants only: previously or currently suffering from clinically significant cardiovascular diseases (except for the hypertension that can be controlled with drugs), or clinically significant disorders related to respiratory system, liver and kidney (except for light fatty liver), gastrointestinal system (except for chronic gastritis), endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix), that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; phase ii/iii participants only: presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix); contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; participants who received other registered investigational drugs of intervention within 1 month before the study vaccination; participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; those who are pregnant or breast-feeding or plan to be pregnant during the study period; those who plan to donate ovum or sperms during the study period; those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; phase i participants only: those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology; phase ii/iii participants only: those who are tested positive for hiv in terms of serology.

a participant who conforms to any of the following criteria should not be enrolled in the study: 1. previous diagnosis of covid-19; 2. phase i participants only: high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; 3. presence of fever within or 72 h before the study vaccination (axillary temperature ≥ 37.3℃); 4. a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; 5. a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; 6. a medical or family history of seizure, epilepsy, encephalopathy and psychosis; 7. immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; 8. long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. 9. patients on antituberculosis therapy; 10. phase i participants only: previously or currently suffering from clinically significant cardiovascular diseases (except for the hypertension that can be controlled with drugs), or clinically significant disorders related to respiratory system, liver and kidney (except for light fatty liver), gastrointestinal system (except for chronic gastritis), endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix), that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; phase ii/iii participants only: presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix); 11. contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; 12. participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; 13. participants who received other registered investigational drugs of intervention within 1 month before the study vaccination; 14. participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; 15. those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; 16. those who are pregnant or breast-feeding or plan to be pregnant during the study period; 17. those who plan to donate ovum or sperms during the study period; 18. those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; 19. those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; 20. phase i participants only: those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology; phase ii/iii participants only: those who are tested positive for hiv in terms of serology.

a participant who conforms to any of the following criteria should not be enrolled in the study: 1. previous diagnosis of covid-19; 2. phase i participants only: high-risk populations (such as medical workers, close contacts of patients with covid-19 infection, etc.) who are more likely to be infected with sars-cov-2; 3. presence of fever within or 72 h before the study vaccination (axillary temperature ≥ 37.3℃); 4. a history of infection or disease related to severe acute respiratory syndrome (sars), middle east respiratory syndrome (mers), or corresponding immunosuppressants; 5. a history of allergic reactions to any vaccine or drug, such as allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, and angioneurotic edema; 6. a medical or family history of seizure, epilepsy, encephalopathy and psychosis; 7. immunocompromised patients suffering from immunodeficiency diseases, important organ diseases, immune diseases (including guillain-barre syndrome [gbs], systemic lupus erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any circumstances, and other immune diseases that may have an impact on immune response in the investigator's opinion), etc.; 8. long-term use of immunosuppressant therapy or immunomodulatory drugs for ≥14 days within the first six months prior to enrollment, or plan to use immunosuppressant therapy or immunomodulatory drugs within two years after enrollment. whereas short-term (≤14 days) use of oral, inhaled and topical steroids are allowed. 9. patients on antituberculosis therapy; 10. phase i participants only: previously or currently suffering from clinically significant cardiovascular diseases (except for the hypertension that can be controlled with drugs), or clinically significant disorders related to respiratory system, liver and kidney (except for light fatty liver), gastrointestinal system (except for chronic gastritis), endocrine system, blood and lymphatic system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix), that may affect the study assessment, or cause risks during the study vaccination, or interfere with the data interpretation as determined by the investigator; phase ii/iii participants only: presence of severe or uncontrollable cardiovascular diseases, or severe or uncontrollable disorders related to endocrine system, blood and lymphatic system, liver and kidney, respiratory system, metabolic and skeletal systems, or malignancies (except for skin basal cell carcinoma and carcinoma in-situ of cervix); 11. contraindications for intramuscular injection or intravenous blood sampling, including thrombocytopenia and other blood coagulation disorders; 12. participants who received any immunoglobulin or blood products in the previous 3 months, or plan to receive similar products during the study; 13. participants who received other registered investigational drugs of intervention within 1 month before the study vaccination; 14. participants vaccinated with influenza vaccine within 14 days or with other vaccines within 28 days before the study vaccination; 15. those who donated blood or had blood loss (≥450 ml) within 3 months before the vaccination or plan to donate blood during the study period; 16. those who are pregnant or breast-feeding or plan to be pregnant during the study period; 17. those who plan to donate ovum or sperms during the study period; 18. those who cannot follow the trial procedures, or cannot cooperate to complete the study due to planned relocation or long-term outing; 19. those unsuitable for participating in the clinical trial as determined by the investigator because of other abnormalities that are likely to confuse the study results, or non-conformance with the maximal benefits of the participants; 20. phase i participants only: those who are tested positive for hepatitis b virus (hbv), hepatitis c virus (hcv), syphilis or hiv in terms of serology; phase ii/iii participants only: those who are tested positive for hiv in terms of serology.