1. use of any investigational medicinal product within 90 days prior to randomization or planned use of such a product during the period of study participation. 2. history of administration of any non-study vaccine within 28 days prior to administration of study vaccine or planned vaccination within 3 months after enrolment. note: receipt of any covid-19 vaccine that is licensed or granted emergency use authorization in vietnam during the course of study participation is not exclusionary if administered after visit 5. 3. previous receipt of investigational vaccine for sars or mers, or any investigational or licensed vaccine that may have an impact on interpretation of the trial results 4. history of hypersensitivity reaction to any prior vaccination or known hypersensitivity to any component of the study vaccine 5. history of egg or chicken allergy 6. history of angioedema 7. history of anaphylaxis (≥ grade 2) 8. acute illness (moderate or severe) and/or fever (body temperature measured orally ≥38°c) 9. any abnormal vital sign deemed clinically relevant by the pi 10. abnormality in screening laboratory test deemed exclusionary by the pi in consultation with the sponsor 11. a positive serologic test for hepatitis b (hbsag) or hepatitis c (hcv ab) (phase 1 only) 12. history of confirmed hiv 13. history of laboratory-confirmed covid-19 14. history of malignancy, excluding non-melanoma skin and cervical carcinoma in situ 15. any confirmed or suspected immunosuppressive or immunodeficient state 16. administration of immunoglobulin or any blood product within 90 days prior to first study injection or planned administration during the study period. 17. administration of any long-acting immune-modifying drugs (e.g., infliximab or rituximab) or the chronic administration (defined as more than 14 days) of immunosuppressants within six months prior to first study injection, or planned administration during the study period (includes systemic corticosteroids at doses equivalent to ≥ 0.5 mg/kg/day of prednisone; the use of topical steroids including inhaled and intranasal steroids is permitted). 18. history of known disturbance of coagulation or blood disorder that could cause anemia or excess bleeding. (e.g, thalassemia, coagulation factor deficiencies). 19. recent history (within the past year) or signs of alcohol or substance abuse. 20. any medical, psychiatric or behavior condition that in the opinion of the pi may interfere with the study objectives, pose a risk to the subject, or prevent the subject from completing the study follow-up. 21. employee of any person employed by the sponsor, the contract research organization (cro), the pi, study site personnel, or site.

1. use of any investigational medicinal product within 90 days prior to randomization or planned use of such a product during the period of study participation. 2. history of administration of any non-study vaccine within 28 days prior to administration of study vaccine or planned vaccination within 3 months after enrolment. note: receipt of any covid-19 vaccine that is licensed or granted emergency use authorization in vietnam during the course of study participation is not exclusionary if administered after visit 5. 3. previous receipt of investigational vaccine for sars or mers, or any investigational or licensed vaccine that may have an impact on interpretation of the trial results 4. history of hypersensitivity reaction to any prior vaccination or known hypersensitivity to any component of the study vaccine 5. history of egg or chicken allergy 6. history of angioedema 7. history of anaphylaxis (≥ grade 2) 8. acute illness (moderate or severe) and/or fever (body temperature measured orally ≥38°c) 9. any abnormal vital sign deemed clinically relevant by the pi 10. abnormality in screening laboratory test deemed exclusionary by the pi in consultation with the sponsor 11. a positive serologic test for hepatitis b (hbsag) or hepatitis c (hcv ab) (phase 1 only) 12. history of confirmed hiv 13. history of laboratory-confirmed covid-19 14. history of malignancy, excluding non-melanoma skin and cervical carcinoma in situ 15. any confirmed or suspected immunosuppressive or immunodeficient state 16. administration of immunoglobulin or any blood product within 90 days prior to first study injection or planned administration during the study period. 17. administration of any long-acting immune-modifying drugs (e.g., infliximab or rituximab) or the chronic administration (defined as more than 14 days) of immunosuppressants within six months prior to first study injection, or planned administration during the study period (includes systemic corticosteroids at doses equivalent to ≥ 0.5 mg/kg/day of prednisone; the use of topical steroids including inhaled and intranasal steroids is permitted). 18. history of known disturbance of coagulation or blood disorder that could cause anemia or excess bleeding. (e.g, thalassemia, coagulation factor deficiencies). 19. recent history (within the past year) or signs of alcohol or substance abuse. 20. any medical, psychiatric or behavior condition that in the opinion of the pi may interfere with the study objectives, pose a risk to the subject, or prevent the subject from completing the study follow-up. 21. employee of any person employed by the sponsor, the contract research organization (cro), the pi, study site personnel, or site.

use of any investigational medicinal product within 90 days prior to randomization or planned use of such a product during the period of study participation. history of administration of any non-study vaccine within 28 days prior to administration of study vaccine or planned vaccination within 3 months after enrolment. note: receipt of any covid-19 vaccine that is licensed or granted emergency use authorization in vietnam during the course of study participation is not exclusionary if administered after visit 5. previous receipt of investigational vaccine for sars or mers, or any investigational or licensed vaccine that may have an impact on interpretation of the trial results history of hypersensitivity reaction to any prior vaccination or known hypersensitivity to any component of the study vaccine history of egg or chicken allergy history of angioedema history of anaphylaxis (≥ grade 2) acute illness (moderate or severe) and/or fever (body temperature measured orally ≥38°c) any abnormal vital sign deemed clinically relevant by the pi abnormality in screening laboratory test deemed exclusionary by the pi in consultation with the sponsor a positive serologic test for hepatitis b (hbsag) or hepatitis c (hcv ab) (phase 1 only) history of confirmed hiv history of laboratory-confirmed covid-19 history of malignancy, excluding non-melanoma skin and cervical carcinoma in situ any confirmed or suspected immunosuppressive or immunodeficient state administration of immunoglobulin or any blood product within 90 days prior to first study injection or planned administration during the study period. administration of any long-acting immune-modifying drugs (e.g., infliximab or rituximab) or the chronic administration (defined as more than 14 days) of immunosuppressants within six months prior to first study injection, or planned administration during the study period (includes systemic corticosteroids at doses equivalent to ≥ 0.5 mg/kg/day of prednisone; the use of topical steroids including inhaled and intranasal steroids is permitted). history of known disturbance of coagulation or blood disorder that could cause anemia or excess bleeding. (e.g, thalassemia, coagulation factor deficiencies). recent history (within the past year) or signs of alcohol or substance abuse. any medical, psychiatric or behavior condition that in the opinion of the pi may interfere with the study objectives, pose a risk to the subject, or prevent the subject from completing the study follow-up. employee of any person employed by the sponsor, the contract research organization (cro), the pi, study site personnel, or site.

use of any investigational medicinal product within 90 days prior to randomization or planned use of such a product during the period of study participation. history of administration of any non-study vaccine within 28 days prior to administration of study vaccine or planned vaccination within 3 months after enrolment. note: receipt of any covid-19 vaccine that is licensed or granted emergency use authorization in vietnam during the course of study participation is not exclusionary if administered after visit 5. previous receipt of investigational vaccine for sars or mers, or any investigational or licensed vaccine that may have an impact on interpretation of the trial results history of hypersensitivity reaction to any prior vaccination or known hypersensitivity to any component of the study vaccine history of egg or chicken allergy history of angioedema history of anaphylaxis (≥ grade 2) acute illness (moderate or severe) and/or fever (body temperature measured orally ≥38°c) any abnormal vital sign deemed clinically relevant by the pi abnormality in screening laboratory test deemed exclusionary by the pi in consultation with the sponsor a positive serologic test for hepatitis b (hbsag) or hepatitis c (hcv ab) (phase 1 only) history of confirmed hiv history of laboratory-confirmed covid-19 history of malignancy, excluding non-melanoma skin and cervical carcinoma in situ any confirmed or suspected immunosuppressive or immunodeficient state administration of immunoglobulin or any blood product within 90 days prior to first study injection or planned administration during the study period. administration of any long-acting immune-modifying drugs (e.g., infliximab or rituximab) or the chronic administration (defined as more than 14 days) of immunosuppressants within six months prior to first study injection, or planned administration during the study period (includes systemic corticosteroids at doses equivalent to ≥ 0.5 mg/kg/day of prednisone; the use of topical steroids including inhaled and intranasal steroids is permitted). history of known disturbance of coagulation or blood disorder that could cause anemia or excess bleeding. (e.g, thalassemia, coagulation factor deficiencies). recent history (within the past year) or signs of alcohol or substance abuse. any medical, psychiatric or behavior condition that in the opinion of the pi may interfere with the study objectives, pose a risk to the subject, or prevent the subject from completing the study follow-up. employee of any person employed by the sponsor, the contract research organization (cro), the pi, study site personnel, or site.