A Blood Collection Study to Assess the Immunogenicity of Nationally Authorized Homologous COVID-19 Booster Vaccines Among Adult Vaccinees.

• 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, 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 of gap prior to first homologous booster vaccination and with no history of other COVID-19 vaccination, including booster doses.
• Participants who complete a qualitative test for antibody to SARS-CoV-2 nucleocapsid proteins at screening for assessment of previous SARS-CoV-2 infection.
• 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 this protocol.

Exclusion Criteria:

• Concurrent or past SARS-CoV-2 infection within 12 weeks prior to the booster study vaccination confirmed by virological or serological testing .
• History of congenital, hereditary, acquired immunodeficiency, or autoimmune disease.
• History of bleeding disorder or thrombocytopenia which is contraindicating to take blood sample.
• History of malignancy within 1 year prior to the screening (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).
• 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 booster vaccination or planned receipt of any vaccine from enrollment through 4 weeks after the booster vaccination, except for influenza vaccination, which may be received at least 2 weeks prior to the booster vaccination.
• 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.
• Participation in another clinical study and 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