A Extension Study to Evaluate the Safety, Tolerability, and Immunogenicity of UB-612 COVID-19 Vaccine

* Inclusion Criteria 1. Male or non-pregnant female who previously participated in and completed two vaccinations in the V-122 Study. 2. Women of childbearing potential and men must agree to practice medically effective contraception during study period. 3. Able to understand the content and possible risks of informed consent and willing to sign the Informed Consent Form (ICF). 4. Able to understand and agrees to comply with all study procedures and be available for all study visits. 5. Ear temperature ≤ 38.0°C. 6. At screening visit, at least 6 months after first vaccination in the V-122 study. * Exclusion Criteria 1. Female who is pregnant or positive in pregnancy test at screening visit. 2. Female who is breast-feeding or plans to breastfeed within 90 days after booster vaccination. 3. Any acute illness, as determined by the study investigator 3 days before booster vaccination. 4. Prior administration of attenuated, nucleic acid (mRNA or DNA) or vectored vaccines in last 1 month before booster vaccination or expectation of such vaccines in the month after booster vaccination. 5. Prior administration of subunit vaccine or inactivated vaccine in last 14 days before booster vaccination or expectation of receipt of such vaccines in the 14 days after booster vaccination. 6. Any medical disease or condition that, in the opinion of the study investigator, may confound the results of the study or pose an additional risk to the subjects by their participation in the study. 7. Previous exposure to SARS-CoV-2 or receipt of an investigational or EUA vaccine product for the prevention of COVID-19, MERS or SARS except UB-612. 8. Subjects who take part in another clinical study, other than V-122 study, within 12 weeks prior to the day of informed consent. 9. Prior administration of immunoglobulins and/or any blood products in last 4 months before booster vaccination. 10. Prior chronic administration of immunosuppressant or corticosteroids, cytotoxic treatment in last 6 months before first vaccination.