1. medical history: history of any of the following diseases or conditions: 1. covid-19; 2. sars; 3. any significant respiratory diseases (e.g. copd, asthma); 4. any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); 5. blood dyscrasias or any significant disorder of coagulation; 6. any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); 7. any chronic infection (e.g. hepatitis b, hepatitis c and hiv); 8. any malignant neoplastic disease; 9. encephalopathy, neuropathy or unstable central nervous system (cns) pathology; 10. any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; 11. any immunodeficiency or autoimmune disease; 12. any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; 13. any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; 14. any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; 15. history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. 2. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: 1. positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); 2. ige level \> 1,000 u.i./ml at screening; 3. positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; 4. t3, t4 or tsh \< lln or \> uln at screening; 5. positive hiv test result at screening; 6. positive hbsag test result at screening; 7. positive hcv antibody test result at screening; 8. positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); 9. positive urine drug screen test result or positive blood alcohol test result at screening or baseline; 10. any clinically significant findings (e.g. active or acute cardiac/pulmonary diseases) from chest x-ray examination performed at or within 4 months prior to screening. 3. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: 1. any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; 2. any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; 3. any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; 4. any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; 5. any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 6. any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 7. regular use of any inhaled/nebulized corticosteroid; 8. any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; 9. any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; 10. any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; 11. donated ≥ 450 ml of blood within 28 days prior to the first vaccination; 12. prior nasal surgery or nasal cauterization. 4. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: 1. prior or current participation in another covid-19 vaccine study; 2. prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; 3. concurrent participation or plan for participation in another interventional clinical study during participation in this study. 5. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. 6. special conditions: existence of any of the following special conditions: 1. close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; 2. travelled outside hong kong within 14 days prior to the first vaccination; 3. planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

1. medical history: history of any of the following diseases or conditions: 1. covid-19; 2. sars; 3. any significant respiratory diseases (e.g. copd, asthma); 4. any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); 5. blood dyscrasias or any significant disorder of coagulation; 6. any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); 7. any chronic infection (e.g. hepatitis b, hepatitis c and hiv); 8. any malignant neoplastic disease; 9. encephalopathy, neuropathy or unstable central nervous system (cns) pathology; 10. any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; 11. any immunodeficiency or autoimmune disease; 12. any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; 13. any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; 14. any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; 15. history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. 2. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: 1. positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); 2. ige level \> 1,000 u.i./ml at screening; 3. positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; 4. t3, t4 or tsh \< lln or \> uln at screening; 5. positive hiv test result at screening; 6. positive hbsag test result at screening; 7. positive hcv antibody test result at screening; 8. positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); 9. positive urine drug screen test result or positive blood alcohol test result at screening or baseline; 10. any clinically significant findings (e.g. active or acute cardiac/pulmonary diseases) from chest x-ray examination performed at or within 4 months prior to screening. 3. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: 1. any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; 2. any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; 3. any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; 4. any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; 5. any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 6. any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 7. regular use of any inhaled/nebulized corticosteroid; 8. any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; 9. any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; 10. any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; 11. donated ≥ 450 ml of blood within 28 days prior to the first vaccination; 12. prior nasal surgery or nasal cauterization. 4. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: 1. prior or current participation in another covid-19 vaccine study; 2. prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; 3. concurrent participation or plan for participation in another interventional clinical study during participation in this study. 5. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. 6. special conditions: existence of any of the following special conditions: 1. close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; 2. travelled outside hong kong within 14 days prior to the first vaccination; 3. planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

medical history: history of any of the following diseases or conditions: covid-19; sars; any significant respiratory diseases (e.g. copd, asthma); any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); blood dyscrasias or any significant disorder of coagulation; any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); any chronic infection (e.g. hepatitis b, hepatitis c and hiv); any malignant neoplastic disease; encephalopathy, neuropathy or unstable central nervous system (cns) pathology; any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; any immunodeficiency or autoimmune disease; any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); ige level > 1,000 u.i./ml at screening; positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; t3, t4 or tsh < lln or > uln at screening; positive hiv test result at screening; positive hbsag test result at screening; positive hcv antibody test result at screening; positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); positive urine drug screen test result or positive blood alcohol test result at screening or baseline; any clinically significant findings (e.g. active or acute cardiac/pulmonary diseases) from chest x-ray examination performed at or within 4 months prior to screening. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; regular use of any inhaled/nebulized corticosteroid; any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; donated ≥ 450 ml of blood within 28 days prior to the first vaccination; prior nasal surgery or nasal cauterization. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: prior or current participation in another covid-19 vaccine study; prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; concurrent participation or plan for participation in another interventional clinical study during participation in this study. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. special conditions: existence of any of the following special conditions: close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; travelled outside hong kong within 14 days prior to the first vaccination; planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

medical history: history of any of the following diseases or conditions: covid-19; sars; any significant respiratory diseases (e.g. copd, asthma); any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); blood dyscrasias or any significant disorder of coagulation; any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); any chronic infection (e.g. hepatitis b, hepatitis c and hiv); any malignant neoplastic disease; encephalopathy, neuropathy or unstable central nervous system (cns) pathology; any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; any immunodeficiency or autoimmune disease; any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); ige level > 1,000 u.i./ml at screening; positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; t3, t4 or tsh < lln or > uln at screening; positive hiv test result at screening; positive hbsag test result at screening; positive hcv antibody test result at screening; positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); positive urine drug screen test result or positive blood alcohol test result at screening or baseline; any clinically significant findings (e.g. active or acute cardiac/pulmonary diseases) from chest x-ray examination performed at or within 4 months prior to screening. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; regular use of any inhaled/nebulized corticosteroid; any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; donated ≥ 450 ml of blood within 28 days prior to the first vaccination; prior nasal surgery or nasal cauterization. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: prior or current participation in another covid-19 vaccine study; prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; concurrent participation or plan for participation in another interventional clinical study during participation in this study. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. special conditions: existence of any of the following special conditions: close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; travelled outside hong kong within 14 days prior to the first vaccination; planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

1. medical history: history of any of the following diseases or conditions: 1. covid-19; 2. sars; 3. any significant respiratory diseases (e.g. copd, asthma); 4. any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); 5. blood dyscrasias or any significant disorder of coagulation; 6. any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); 7. any chronic infection (e.g. hepatitis b, hepatitis c and hiv); 8. any malignant neoplastic disease; 9. encephalopathy, neuropathy or unstable central nervous system (cns) pathology; 10. any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; 11. any immunodeficiency or autoimmune disease; 12. any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; 13. any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; 14. any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; 15. history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. 2. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: 1. positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); 2. ige level > 1,000 u.i./ml at screening; 3. positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; 4. t3, t4 or tsh < lln or > uln at screening; 5. positive hiv test result at screening; 6. positive hbsag test result at screening; 7. positive hcv antibody test result at screening; 8. positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); 9. positive urine drug screen test result or positive blood alcohol test result at screening or baseline; 10. any clinically significant findings (e.g. active or acute cardiac/pulmonary diseases) from chest x-ray examination performed at or within 4 months prior to screening. 3. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: 1. any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; 2. any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; 3. any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; 4. any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; 5. any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 6. any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 7. regular use of any inhaled/nebulized corticosteroid; 8. any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; 9. any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; 10. any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; 11. donated ≥ 450 ml of blood within 28 days prior to the first vaccination; 12. prior nasal surgery or nasal cauterization. 4. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: 1. prior or current participation in another covid-19 vaccine study; 2. prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; 3. concurrent participation or plan for participation in another interventional clinical study during participation in this study. 5. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. 6. special conditions: existence of any of the following special conditions: 1. close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; 2. travelled outside hong kong within 14 days prior to the first vaccination; 3. planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

1. medical history: history of any of the following diseases or conditions: 1. covid-19; 2. sars; 3. any significant respiratory diseases (e.g. copd, asthma); 4. any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); 5. blood dyscrasias or any significant disorder of coagulation; 6. any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); 7. any chronic infection (e.g. hepatitis b, hepatitis c and hiv); 8. any malignant neoplastic disease; 9. encephalopathy, neuropathy or unstable central nervous system (cns) pathology; 10. any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; 11. any immunodeficiency or autoimmune disease; 12. any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; 13. any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; 14. any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; 15. history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. 2. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: 1. positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); 2. ige level > 1,000 u.i./ml at screening; 3. positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; 4. t3, t4 or tsh < lln or > uln at screening; 5. positive hiv test result at screening; 6. positive hbsag test result at screening; 7. positive hcv antibody test result at screening; 8. positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); 9. positive urine drug screen test result or positive blood alcohol test result at screening or baseline; 10. any clinically significant findings (e.g. active or acute cardiac/pulmonary diseases) from chest x-ray examination performed at or within 4 months prior to screening. 3. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: 1. any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; 2. any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; 3. any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; 4. any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; 5. any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 6. any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 7. regular use of any inhaled/nebulized corticosteroid; 8. any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; 9. any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; 10. any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; 11. donated ≥ 450 ml of blood within 28 days prior to the first vaccination; 12. prior nasal surgery or nasal cauterization. 4. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: 1. prior or current participation in another covid-19 vaccine study; 2. prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; 3. concurrent participation or plan for participation in another interventional clinical study during participation in this study. 5. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. 6. special conditions: existence of any of the following special conditions: 1. close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; 2. travelled outside hong kong within 14 days prior to the first vaccination; 3. planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

1. medical history: history of any of the following diseases or conditions: 1. covid-19; 2. sars; 3. any significant respiratory diseases (e.g. copd, asthma); 4. any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); 5. blood dyscrasias or any significant disorder of coagulation; 6. any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); 7. any chronic infection (e.g. hepatitis b, hepatitis c and hiv); 8. any malignant neoplastic disease; 9. encephalopathy, neuropathy or unstable central nervous system (cns) pathology; 10. any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; 11. any immunodeficiency or autoimmune disease; 12. any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; 13. any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; 14. any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; 15. history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. 2. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: 1. positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); 2. ige level > 1,000 u.i./ml at screening; 3. positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; 4. t3, t4 or tsh < lln or > uln at screening; 5. positive hiv test result at screening; 6. positive hbsag test result at screening; 7. positive hcv antibody test result at screening; 8. positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); 9. positive urine drug screen test result or positive blood alcohol test result at screening or baseline; 10. any clinical significant findings (e.g. active or acute cardiac/pulmonary diseases) of chest x-ray at screening. 3. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: 1. any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; 2. any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; 3. any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; 4. any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; 5. any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 6. any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 7. regular use of any inhaled/nebulized corticosteroid; 8. any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; 9. any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; 10. any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; 11. donated ≥ 450 ml of blood within 28 days prior to the first vaccination; 12. prior nasal surgery or nasal cauterization. 4. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: 1. prior or current participation in another covid-19 vaccine study; 2. prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; 3. concurrent participation or plan for participation in another interventional clinical study during participation in this study. 5. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. 6. special conditions: existence of any of the following special conditions: 1. close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; 2. travelled outside hong kong within 14 days prior to the first vaccination; 3. planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.

1. medical history: history of any of the following diseases or conditions: 1. covid-19; 2. sars; 3. any significant respiratory diseases (e.g. copd, asthma); 4. any significant cardiovascular disease (e.g. angina, cardiac arrhythmias); 5. blood dyscrasias or any significant disorder of coagulation; 6. any chronic liver disease (e.g. autoimmune hepatitis and cirrhosis); 7. any chronic infection (e.g. hepatitis b, hepatitis c and hiv); 8. any malignant neoplastic disease; 9. encephalopathy, neuropathy or unstable central nervous system (cns) pathology; 10. any psychiatric disorder, psychotic disorder, major affective disorder or suicidal ideation; 11. any immunodeficiency or autoimmune disease; 12. any severe allergic reaction (e.g. anaphylaxis) to any vaccine or substance, which requires hospitalization or emergency medical care; 13. any hypersensitivity to (especially anaphylactic reactions) to eggs, egg proteins or gentamicin sulfate; 14. any chronic rhinitis, nasal septal defect, cleft palate, nasal polyps or other nasal abnormality that might affect vaccine administration; 15. history of alcohol or illicit drug abuse, or used any illicit drug within 6 months prior to screening. 2. medical conditions or diagnoses: existence of any of the following medical conditions or diagnoses: 1. positive serum pregnancy test at screening or positive urine pregnancy test at baseline (for wocbp); 2. ige level > 1,000 u.i./ml at screening; 3. positive sars-cov-2 test result in serum, deep throat saliva (dts) or nasopharyngeal swab (nps) within 4 days prior to baseline; 4. t3, t4 or tsh < lln or > uln at screening; 5. positive hiv test result at screening; 6. positive hbsag test result at screening; 7. positive hcv antibody test result at screening; 8. positive t-cell interferon-γ release assay (tigra) result (i.e. by quantiferon®-tb gold plus™ test) at screening (remark: a single repeat will be allowed with an indeterminate result); 9. positive urine drug screen test result or positive blood alcohol test result at screening or baseline; 10. any clinical significant findings (e.g. active or acute cardiac/pulmonary diseases) of chest x-ray at screening. 3. prior/concomitant interventions: use of or undergoing any of the following prior or concomitant medications, therapies or interventions: 1. any covid-19 or coronavirus vaccine at any time prior to the first vaccination, or planned use of any such vaccine throughout the study; 2. any vaccine other than covid-19 or coronavirus vaccines within 28 days prior to the first vaccination, or planned use of any such vaccine up to 28 days after the second vaccination; 3. any immune-modifying medication/therapy (e.g. immunomodulator and immunosuppressant) within 6 months prior to the first vaccination, or planned use of any such medication/therapy throughout the study; 4. any blood product (including blood transfusion) or immunoglobulin within 3 months prior to the first vaccination, or planned use of any such therapy throughout the study; 5. any anticoagulation medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 6. any psychotropic medication within 28 days prior to the first vaccination, or planned use of any such medication up to 28 days after the second vaccination; 7. regular use of any inhaled/nebulized corticosteroid; 8. any intranasal preparation within 48 hours prior to the first vaccination, or planned use of any such preparation up to 48 hours after the second vaccination; 9. any influenza antiviral medication within 48 hours prior to the first vaccination, or planned use of any such medication up to 14 days after the second vaccination; 10. any prescription or over-the-counter medication or supplement product (e.g. vitamin, dietary supplement, herbal preparation) within 7 days prior to the first vaccination, unless with the investigator's approval for managing a chronic condition; 11. donated ≥ 450 ml of blood within 28 days prior to the first vaccination; 12. prior nasal surgery or nasal cauterization. 4. prior/concurrent clinical study: prior or concurrent participation in any other clinical study, including: 1. prior or current participation in another covid-19 vaccine study; 2. prior participation in any interventional clinical study and use of any investigational intervention within 90 days prior to the first vaccination; 3. concurrent participation or plan for participation in another interventional clinical study during participation in this study. 5. other significant medical conditions: any clinically significant concomitant disease or condition that, in the reasonable opinion of the investigator, may interfere with the subject's participation in this study or pose an unacceptable safety risk for the subject's participation in this study. 6. special conditions: existence of any of the following special conditions: 1. close contact with anyone known to have covid-19 within 30 days prior to the first vaccination; 2. travelled outside hong kong within 14 days prior to the first vaccination; 3. planned to travel outside hong kong at any time during the period from screening to day 57(±3) visit.