Platform Trial to Compare Homologous Boost of Authorized COVID-19 Vaccines and Heterologous Boost With UB-612 Vaccine

Inclusion Criteria: 1. Signed and dated informed consent/assent after reading the consent/assent form and having adequate opportunity to discuss the study with an investigator or designee. 2. Documented fully vaccinated with primary series of a comparator vaccine. Primary immunization is defined as 2 doses spaced approximately 3-16 weeks apart. The last dose of the previous vaccine must have been administered at least three (3) months (Pfizer at least (5) months) prior to Day 1, taking into consideration the current local and national regulations, and according to details related to individual comparators provided in relevant sub-studies. Documentation, such as the National Health Service (NHS) COVID Pass, United States Centers for Disease Control vaccine card, or equivalent documentation (e.g., medical records, vaccine passport; in accordance with local approved vaccination record documentation) will be required for proof of vaccination, vaccine manufacturer and vaccination dates. 3. No clinically significant health problems that could affect the safety of the subject, as determined by the investigator by medical history, laboratory tests and physical examination. May have a stable pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before screening or which, in the judgement of the investigator is unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after Day 1. 4. Negative SARS-CoV-2 reverse transcriptase-polymerase chain reaction (RT-PCR) or antigen test within 24-48 hours prior to receipt of injections on Day 1. 5. Female subjects of non-childbearing potential may be enrolled. 6. Males and WOCBP, 16 years or older, may be enrolled in the study if they are willing to practice abstinence from sexual intercourse or are willing to use acceptable methods of contraception as described below, from the time of signing the informed consent/assent during the screening period through study product injection on Day 1 and until completion of Day 29. Acceptable methods of contraception should be consistent with local availability/regulations regarding the use of contraceptive methods for those participating in clinical trials. 7. For WOCBP, a serum or urine pregnancy test must be negative at Screening and on the day of study product injection. 8. Must be able to read, understand, and complete questionnaires and diary entries. 9. Plans to reside within study area for the duration of the study. 10. Able to comply with study procedures for the full duration of the study, in the opinion of the investigator. Exclusion Criteria: 1. Known history of COVID-19 or SARS-CoV-2 infection within six (6) months prior to vaccination (Day 1). 2. Receipt of a booster COVID-19 vaccination in addition to the primary vaccine series. 3. Presence of fever \>100.4°F/38°C or other signs or symptoms of COVID-19 (e.g., chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, or diarrhea) within 1 week prior to Day 1 study product injection. Screening and/or study product injection may be rescheduled at the discretion of the investigator. 4. Clinical manifestations of systemic diseases considered by the investigator to impact safety or immunogenicity. 5. Prior history of pericarditis or myocarditis of any etiology. 6. Prior history of thrombosis of major vessels, including cerebrovascular or splanchnic thrombosis or of thrombosis with thrombocytopenia syndrome 7. History of anaphylaxis (vaccine related or not). 8. Chronic kidney disease with dialysis. 9. Receipt of systemic corticosteroids (≥0.5 mg/kg per day of prednisone or equivalent)for ≥7 days is prohibited from 28 days before enrollment through conclusion of the study. Topical, inhaled, intra-nasal, intra-articular or intra-bursal administration of corticosteroids is permitted. 10. Receipt of any cytotoxic or immunosuppressive drug or biologics six (6) months prior to Day 1 visit. 11. Receipt of any investigational drug within six (6) months prior to Day 1 visit. 12. Subject received or plans to receive a live attenuated vaccine or licensed adjuvanted(non-aluminum compound) vaccination within 28 days before or after planned administration of study vaccine (Day 1) or another type of vaccine (including influenza vaccine) within 14 days prior to or after planned administration of study vaccine on Day1 visit. 13. Human immunodeficiency virus (HIV) or hepatitis B surface antigen (HBsAg) positive; hepatitis C virus (HCV) antibody positive subjects may be tested for RNA and if negative may be enrolled. 14. Any Grade 2 or greater clinical or laboratory abnormalities at screening results. Grade 1 abnormal clinical or laboratory adverse event screening test results which, according to the investigator, are non-clinically significant would not disqualify a potential subject. Clinical or laboratory screening tests may be repeated once to exclude transient abnormalities. 15. Immunocompromised state (weakened immune system) from solid organ transplant, immunosuppressive or immunodeficient state, autoimmune diseases, asplenia and, recurrent severe infections. 16. Have an active malignancy or history of metastatic or hematologic malignancy except non-melanoma skin cancers. 17. Pregnant or breastfeeding female, or female who intends to become pregnant during the study period. 18. Administration of immunoglobulins and/or any blood products within the 120 days preceding Day 1 or planned administration during the study period. 19. Bleeding disorder considered a contraindication to intramuscular injection or phlebotomy. 20. Bilateral tattoos or scars at the deltoid sites of intramuscular (IM) injection that would obscure examination of injection site reactions. 21. Behavioral, cognitive, or psychiatric disease that, in the opinion of the Principal Investigator or his or her representative physician, affects the subject's ability to understand and cooperate with all study protocol requirements. 22. Any alcohol or drug abuse over the 12 months prior to enrollment in the study that has caused medical, professional, or family problems, indicated by clinical history. 23. Grade 2 or higher hypertension (systolic \>160 mm Hg and/or diastolic \>100 mm Hg). 24. Any other condition that, in the opinion of the Principal Investigator or his/her representative physician, could put the safety/rights of potential subjects at risk or prevent them from complying with the study protocol.