Immunogenicity and Safety Study of SK SARS-CoV-2 Recombinant Nanoparticle Vaccine (GBP510) Adjuvanted With AS03 (COVID-19)

Inclusion Criteria: * Participant must be 18 years of age and older, at the time of signing the informed consent; * Participants who are healthy or medically stable as determined by medical evaluation including medical history, physical examination, clinical laboratory tests, and medical judgement of the investigator; * Participants who are able to attend all scheduled visits and comply with all study procedures; * Female participants of childbearing potential must agree to be heterosexually inactive, or agree to consistently use at least one acceptable method of contraception from at least 4 weeks prior to the 1st study vaccination to 12 weeks after the last study vaccination; * Female participants with a negative urine or serum pregnancy test at screening; * Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in protocol; \<Stage2\> * Participants who have received 2 doses of GBP510 25μg adjuvanted with AS03 or ChAdOx1-S and have blood samples until Visit 7 in Stage 1 * Participants who received a primary series of GBP510 or ChAdOx1-S at least 12 weeks prior to booster vaccination in Stage 2 * Participants who are able to attend all additionally scheduled visits and comply with all study procedures. * Female participants of childbearing potential must agree to be heterosexually inactive, or agree to consistently use at least one acceptable method of contraception from at least 4 weeks prior to the booster dose (3rd study vaccination) to 12 weeks after the booster dose * Female participants with a negative urine or serum pregnancy test prior to the booster dose (the third dose of study vaccine) * Capable of giving an informed consent for Stage 2 study in compliance with the requirements and restrictions listed in the informed consent form (ICF) for Stage 2 and in this protocol. Exclusion Criteria: * 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.