* any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature \>38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; * (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; * history of virologically-confirmed sars or mers disease, or sars / mers vaccination; * history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; * history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; * history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; * history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); * significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; * any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); * female participants who are pregnant or breastfeeding; * receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; * receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; * receipt of any medications or vaccinations intended to prevent covid-19; * chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted; * participation in another clinical study involving study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period. * participants who are subjected to any global or local restrictions in place for use of chadox1-s (e.g. age, gender, or other specific population groups) * investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members. \<stage2\> * any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature \>38°c), or acute illness within 72 hours prior to the booster dose (3rd study vaccination). a prospective participant should not be included until 72 hours after the condition has resolved. * history of confirmed covid-19, sars or mers disease confirmed by serological, virological assay, or rapid antigen kit * receipt of any medications or vaccinations intended to prevent covid-19 except for gbp510 or chadox1-s. * receipt of any vaccine within 4 weeks prior to the booster vaccination or planned receipt of any vaccine from enrollment through 28 days after the booster vaccination (visit 4b), except for influenza vaccination, which may be received at least 2 weeks prior to the booster vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines * receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the booster vaccination * chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the booster vaccination. the use of topical and nasal glucocorticoids will be permitted.

* any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature \>38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; * (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; * history of virologically-confirmed sars or mers disease, or sars / mers vaccination; * history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; * history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; * history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; * history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); * significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; * any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); * female participants who are pregnant or breastfeeding; * receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; * receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; * receipt of any medications or vaccinations intended to prevent covid-19; * chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted; * participation in another clinical study involving study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period. * participants who are subjected to any global or local restrictions in place for use of chadox1-s (e.g. age, gender, or other specific population groups) * investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members. \<stage2\> * any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature \>38°c), or acute illness within 72 hours prior to the booster dose (3rd study vaccination). a prospective participant should not be included until 72 hours after the condition has resolved. * history of confirmed covid-19, sars or mers disease confirmed by serological, virological assay, or rapid antigen kit * receipt of any medications or vaccinations intended to prevent covid-19 except for gbp510 or chadox1-s. * receipt of any vaccine within 4 weeks prior to the booster vaccination or planned receipt of any vaccine from enrollment through 28 days after the booster vaccination (visit 4b), except for influenza vaccination, which may be received at least 2 weeks prior to the booster vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines * receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the booster vaccination * chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the booster vaccination. the use of topical and nasal glucocorticoids will be permitted.

any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; history of virologically-confirmed sars or mers disease, or sars / mers vaccination; history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); female participants who are pregnant or breastfeeding; receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; receipt of any medications or vaccinations intended to prevent covid-19; chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted; participation in another clinical study involving study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period. participants who are subjected to any global or local restrictions in place for use of chadox1-s (e.g. age, gender, or other specific population groups) investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members. <stage2> any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the booster dose (3rd study vaccination). a prospective participant should not be included until 72 hours after the condition has resolved. history of confirmed covid-19, sars or mers disease confirmed by serological, virological assay, or rapid antigen kit receipt of any medications or vaccinations intended to prevent covid-19 except for gbp510 or chadox1-s. receipt of any vaccine within 4 weeks prior to the booster vaccination or planned receipt of any vaccine from enrollment through 28 days after the booster vaccination (visit 4b), except for influenza vaccination, which may be received at least 2 weeks prior to the booster vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the booster vaccination chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the booster vaccination. the use of topical and nasal glucocorticoids will be permitted.

any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; history of virologically-confirmed sars or mers disease, or sars / mers vaccination; history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); female participants who are pregnant or breastfeeding; receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; receipt of any medications or vaccinations intended to prevent covid-19; chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted; participation in another clinical study involving study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period. participants who are subjected to any global or local restrictions in place for use of chadox1-s (e.g. age, gender, or other specific population groups) investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members. <stage2> any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the booster dose (3rd study vaccination). a prospective participant should not be included until 72 hours after the condition has resolved. history of confirmed covid-19, sars or mers disease confirmed by serological, virological assay, or rapid antigen kit receipt of any medications or vaccinations intended to prevent covid-19 except for gbp510 or chadox1-s. receipt of any vaccine within 4 weeks prior to the booster vaccination or planned receipt of any vaccine from enrollment through 28 days after the booster vaccination (visit 4b), except for influenza vaccination, which may be received at least 2 weeks prior to the booster vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the booster vaccination chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the booster vaccination. the use of topical and nasal glucocorticoids will be permitted.

- any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; - (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; - history of virologically-confirmed sars or mers disease, or sars / mers vaccination; - history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; - history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; - history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; - history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); - significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; - any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); - female participants who are pregnant or breastfeeding; - receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; - receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; - receipt of any medications or vaccinations intended to prevent covid-19; - chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted; - participation in another clinical study involving study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period. - participants who are subjected to any global or local restrictions in place for use of chadox1-s (e.g. age, gender, or other specific population groups) - investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members.

- any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; - (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; - history of virologically-confirmed sars or mers disease, or sars / mers vaccination; - history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; - history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; - history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; - history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); - significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; - any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); - female participants who are pregnant or breastfeeding; - receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; - receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; - receipt of any medications or vaccinations intended to prevent covid-19; - chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted; - participation in another clinical study involving study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period. - participants who are subjected to any global or local restrictions in place for use of chadox1-s (e.g. age, gender, or other specific population groups) - investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members.

- any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; - (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; - history of virologically-confirmed sars or mers disease, or sars / mers vaccination; - history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; - history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; - history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; - history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); - significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; - any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); - female participants who are pregnant or breastfeeding; - receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; - receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; - receipt of any medications or vaccinations intended to prevent covid-19; - chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted;

- any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°c), or acute illness within 72 hours prior to the 1st study vaccination. a prospective participant should not be included until 72 hours after the condition has resolved; - (only for cohort 1) prior sars-cov-2 infection or vaccination confirmed by a positive result of qualitative test for sars-cov-2 antibody using a rapid antibody kit at screening; - history of virologically-confirmed sars or mers disease, or sars / mers vaccination; - history of congenital, hereditary, acquired immunodeficiency, or autoimmune disease; - history of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination; - history of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, guillain-barre syndrome) to any vaccines or components of the study vaccine; - history of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator); - significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results; - any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions); - female participants who are pregnant or breastfeeding; - receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 28 days after the last study vaccination (visit 7), except for influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination. this exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines; - receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the 1st study vaccination; - receipt of any medications or vaccinations intended to prevent covid-19; - chronic use (more than 2 consecutive weeks) of immunosuppressive therapy, such as anticancer chemotherapy or radiation therapy; or long-term systemic corticosteroid therapy (≥10mg prednisone/day or equivalent for more than 2 consecutive weeks) within 12 weeks prior to the 1st vaccination. the use of topical and nasal glucocorticoids will be permitted;