This is a Phase III, randomized, placebo-controlled, observer-blinded, parallel-group, multi-center study to assess the safety, reactogenicity, and immunogenicity of heterologous booster vaccination of SK SARS-CoV-2 recombinant protein nanoparticle vaccine (GBP510) adjuvanted with AS03 in adults aged 18 years and older.

The purpose of this study is to assess the safety, reactogenicity, and immunogenicity of heterologous booster vaccination of a SARS-CoV-2 Recombinant Protein Nanoparticle Vaccine (GBP510) adjuvanted with AS03 in adults aged 18 years and older.

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.
• Participants who received primary vaccination of 1 of 6 different WHO EUA qualified COVID-19 vaccine (mRNA-1273, ChAdOx1 nCOV-19, Ad26.COV2.S, BNT162b2, BBIBP-CorV, CoronaVac) at least 12 weeks prior to study vaccination, and with no history of other COVID-19 vaccination, including booster doses.
• Participants who have a qualitative test result for antibody to SARS-CoV-2 nucleocapsid proteins at screening for assessment of previous SARS-CoV-2 infection
• 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 study vaccination to 12 weeks after the study vaccination
• Female participants with a negative urine or serum pregnancy test at screening.
• Capable of giving signed informed consent as described in Appendix 10.1.3 which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) 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 study vaccination. A prospective participant should not be included until 72 hours after the condition has resolved.
• Concurrent or past SARS-CoV-2 infection within 12 weeks prior to the study vaccination confirmed by virological or serological testing
• History of virologically or serologically confirmed SARS, or MERS disease
• History of congenital, hereditary, acquired immunodeficiency, or autoimmune disease.
• History of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination in the investigator's opinion.
• History of hypersensitivity and severe allergic reaction (e.g. anaphylaxis, Guillain-Barre syndrome) to any vaccines or components of the study intervention.
• History of malignancy within 1 year prior to the 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 medications or vaccinations intended to prevent COVID-19 except for the pre-defined COVID-19 vaccines expected to be given prior to screening (mRNA-1273, ChAdOx1 nCOV-19, Ad26.COV2.S, BNT162b2, BBIBP-CorV, CoronaVac).
• Receipt of any vaccine within 4 weeks prior to the study vaccination or planned receipt of any vaccine from enrollment through 4 weeks after the study vaccination, except for influenza vaccination, which may be received at least 2 weeks prior to the study vaccination.
• Receipt of immunoglobulins and/or any blood or blood products within 12 weeks prior to the study 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 study vaccination. The use of topical and nasal glucocorticoids will be permitted.
• Participation in another clinical study and receipt of study intervention within 4 weeks prior to the study vaccination, or concurrent, planned participation in another clinical study with study intervention during the study period.
• Investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members.
• Donation of ≥450mL of blood product within 4 weeks prior to screening, or planned donation of blood product during the study period