Immunogenicity and Safety Study of SCB-2023 Vaccine as a Booster in Adults

Inclusion Criteria: * Male or female ≥18 years of age. * Individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests and other study procedures. * Individuals willing and able to give an informed consent, prior to screening. * Healthy participants or participants with pre-existing medical conditions who are in a stable medical condition. * Individuals who received three doses of inactivated COVID-19 vaccine. Exclusion Criteria: * Body temperature \>37.8°C (axillary), or any acute illness at baseline. * Confirmed SARS-CoV-2 infectionor with known history of COVID-19. * Individuals who have received an investigational or licensed COVID-19 vaccine prior to Day 1 (except for inactivated COVID-19 vaccine). * Any confirmed or suspected immunosuppressive or immunodeficient condition resulting from disease or immunosuppressive/cytotoxic therapy. * Any progressive unstable or uncontrolled clinical conditions. * Individuals who are pregnant, or breastfeeding, or planning to become pregnant while enrolled in this study or during the study period. * History of severe adverse reaction associated with a vaccine or severe allergic reaction. * History of malignancy within 1 year before screening. * Individuals who have received any other investigational product. * Individuals who have received any other licensed vaccines within 14 days prior to enrollment. * Treatment with Rituximab or any other anti-CD20 monoclonal antibodies. * Known bleeding disorder that would, in the opinion of the investigator, contraindicate i.m. injection. * Administration of intravenous immunoglobulins and/or any blood products. * Any condition that, in the opinion of the investigator, would interfere with the primary study objectives or pose additional risk to the participant.