Mix and Match Heterologous Prime-Boost Study Using Approved COVID-19 Vaccines

Inclusion Criteria: * Individuals aged 18 to 65 years old at the time of consent. * Residing within the area of the study and planning to stay for the study duration. * HIV negative test result on the day of screening (for those who do not have a documented HIV test results in the last three months of screening). * Female volunteers of childbearing potential with a negative pregnancy test on the day(s) of screening and vaccination, practicing/willing to practice continuous effective contraception\* recommended by the National Health System up to 12 weeks after the booster vaccination.. * Agreement to refrain from blood donation during the course of the study. * Able and willing to comply with all study requirements, based on the assessment of the investigator. * Willingness to provide written informed consent before any trial procedure \* Effective contraception is defined as follows: contraceptive medications delivered orally, intramuscularly, vaginally, or implanted underneath the skin, surgical methods (hysterectomy or bilateral tubal ligation), condoms, diaphragms, intrauterine device (IUD), and abstinence. Exclusion Criteria: * Pregnancy, lactation, or intention to become pregnant during the vaccination phase through three months after the booster dose. * Prior receipt/ planned receipt of any vaccine other than the study intervention within 28 days before and after each study vaccination. * Previous participation in any COVID-19 vaccination trial or vaccination campaign. * Administration of immunoglobulins and/ or any blood products within the three months preceding the administration of the study vaccine. * Known infection with hepatitis B, C virus. * Known history of allergy or anaphylaxis to study vaccine components and/or excipients or other medications, or any other allergies deemed by the investigator to increase the risk of an adverse reaction. * History of bleeding disorder (e.g., factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venipuncture. * Continuous use of the anticoagulants, such as coumarins and related anticoagulants. * Severe and/or uncontrolled cardiovascular disease, respiratory disease, gastrointestinal disease, renal disease, liver disease, endocrine disorders, and neurological illness (mild/moderate well controlled comorbidities are allowed). * Any clinically significant abnormal finding on screening as judged by the investigator. * Confirmed SARS-CoV-2 infection at enrollment. * Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections and chronic use (more than 14 days) immunosuppressant medication within 3 months prior to recruitment (topical steroids are allowed). * Any other finding which in the opinion of the investigators would increase the risk of an adverse outcome from participation in the trial or result in incomplete or poor-quality data.