1. those who have already received a third dose of sars-cov-2 vaccine 2. concomitantly enrolled or scheduled to be enrolled in another trial. 3. those with fever (temperature ˃ 37.5℃, measured with infrared thermometer/thermal gun), upper respiratory tract infection symptoms such as sneezing, nasal congestion, runny nose, cough, sore throat, loss of taste, chills and shortness of breath within 72 hours before enrolment. 4. blood pressure ˃ 180/110 mmhg. 5. history of confirmed covid-19 within one month prior to study enrolment. 6. history of allergy to vaccines or vaccine ingredients, and severe adverse reactions to vaccines, such as urticaria, dyspnoea, and angioneurotic oedema. 7. those with uncontrolled autoimmune disease such as systemic lupus erythematosis. 8. history of uncontrolled coagulopathy or blood disorders, immune deficiency. 9. history of having received blood derived product/transfusion within 3 months prior to enrolment. 10. those who received immunosuppressant therapy such as high-dose corticosteroid or cancer chemotherapy 11. those with uncontrolled chronic disease, such as severe heart disease, asthma exacerbation 12. those who have history of uncontrolled epilepsy (within the last 2 years) or other progressive neurological disorders, such as guillain-barre syndrome 13. those who have receive any vaccination within 2 weeks before study vaccine administration for this protocol, or intended to receive any vaccination within 2 weeks after study vaccine administration. 14. pregnant woman 15. those aged ≥60 years old with difficulty in climbing 10 steps of stairs, frequently experiencing fatigue, difficulty in walking 100-200 m, or having at least 5 comorbidities (hypertension, diabetes, cancer, chronic lung disease, heart attack, congestive heart failure, chest pain, asthma, joint pain, stroke, and kidney disease). 16. those who are study staff working on the study or the immediate family of study investigators

1. those who have already received a third dose of sars-cov-2 vaccine 2. concomitantly enrolled or scheduled to be enrolled in another trial. 3. those with fever (temperature ˃ 37.5℃, measured with infrared thermometer/thermal gun), upper respiratory tract infection symptoms such as sneezing, nasal congestion, runny nose, cough, sore throat, loss of taste, chills and shortness of breath within 72 hours before enrolment. 4. blood pressure ˃ 180/110 mmhg. 5. history of confirmed covid-19 within one month prior to study enrolment. 6. history of allergy to vaccines or vaccine ingredients, and severe adverse reactions to vaccines, such as urticaria, dyspnoea, and angioneurotic oedema. 7. those with uncontrolled autoimmune disease such as systemic lupus erythematosis. 8. history of uncontrolled coagulopathy or blood disorders, immune deficiency. 9. history of having received blood derived product/transfusion within 3 months prior to enrolment. 10. those who received immunosuppressant therapy such as high-dose corticosteroid or cancer chemotherapy 11. those with uncontrolled chronic disease, such as severe heart disease, asthma exacerbation 12. those who have history of uncontrolled epilepsy (within the last 2 years) or other progressive neurological disorders, such as guillain-barre syndrome 13. those who have receive any vaccination within 2 weeks before study vaccine administration for this protocol, or intended to receive any vaccination within 2 weeks after study vaccine administration. 14. pregnant woman 15. those aged ≥60 years old with difficulty in climbing 10 steps of stairs, frequently experiencing fatigue, difficulty in walking 100-200 m, or having at least 5 comorbidities (hypertension, diabetes, cancer, chronic lung disease, heart attack, congestive heart failure, chest pain, asthma, joint pain, stroke, and kidney disease). 16. those who are study staff working on the study or the immediate family of study investigators

those who have already received a third dose of sars-cov-2 vaccine concomitantly enrolled or scheduled to be enrolled in another trial. those with fever (temperature ˃ 37.5℃, measured with infrared thermometer/thermal gun), upper respiratory tract infection symptoms such as sneezing, nasal congestion, runny nose, cough, sore throat, loss of taste, chills and shortness of breath within 72 hours before enrolment. blood pressure ˃ 180/110 mmhg. history of confirmed covid-19 within one month prior to study enrolment. history of allergy to vaccines or vaccine ingredients, and severe adverse reactions to vaccines, such as urticaria, dyspnoea, and angioneurotic oedema. those with uncontrolled autoimmune disease such as systemic lupus erythematosis. history of uncontrolled coagulopathy or blood disorders, immune deficiency. history of having received blood derived product/transfusion within 3 months prior to enrolment. those who received immunosuppressant therapy such as high-dose corticosteroid or cancer chemotherapy those with uncontrolled chronic disease, such as severe heart disease, asthma exacerbation those who have history of uncontrolled epilepsy (within the last 2 years) or other progressive neurological disorders, such as guillain-barre syndrome those who have receive any vaccination within 2 weeks before study vaccine administration for this protocol, or intended to receive any vaccination within 2 weeks after study vaccine administration. pregnant woman those aged ≥60 years old with difficulty in climbing 10 steps of stairs, frequently experiencing fatigue, difficulty in walking 100-200 m, or having at least 5 comorbidities (hypertension, diabetes, cancer, chronic lung disease, heart attack, congestive heart failure, chest pain, asthma, joint pain, stroke, and kidney disease). those who are study staff working on the study or the immediate family of study investigators

those who have already received a third dose of sars-cov-2 vaccine concomitantly enrolled or scheduled to be enrolled in another trial. those with fever (temperature ˃ 37.5℃, measured with infrared thermometer/thermal gun), upper respiratory tract infection symptoms such as sneezing, nasal congestion, runny nose, cough, sore throat, loss of taste, chills and shortness of breath within 72 hours before enrolment. blood pressure ˃ 180/110 mmhg. history of confirmed covid-19 within one month prior to study enrolment. history of allergy to vaccines or vaccine ingredients, and severe adverse reactions to vaccines, such as urticaria, dyspnoea, and angioneurotic oedema. those with uncontrolled autoimmune disease such as systemic lupus erythematosis. history of uncontrolled coagulopathy or blood disorders, immune deficiency. history of having received blood derived product/transfusion within 3 months prior to enrolment. those who received immunosuppressant therapy such as high-dose corticosteroid or cancer chemotherapy those with uncontrolled chronic disease, such as severe heart disease, asthma exacerbation those who have history of uncontrolled epilepsy (within the last 2 years) or other progressive neurological disorders, such as guillain-barre syndrome those who have receive any vaccination within 2 weeks before study vaccine administration for this protocol, or intended to receive any vaccination within 2 weeks after study vaccine administration. pregnant woman those aged ≥60 years old with difficulty in climbing 10 steps of stairs, frequently experiencing fatigue, difficulty in walking 100-200 m, or having at least 5 comorbidities (hypertension, diabetes, cancer, chronic lung disease, heart attack, congestive heart failure, chest pain, asthma, joint pain, stroke, and kidney disease). those who are study staff working on the study or the immediate family of study investigators