Clinical Trial to Study the COVAC-2 Booster Dose (for COVID-19) in Generally Healthy Adults.

Inclusion Criteria: * Generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. * Good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. Note: Participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the Investigator. A stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. Also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. Mild to moderate well-controlled comorbidities are allowed. * Have received minimum of 2 doses of an authorized COVID-19 vaccine at least 4 months prior to Day 0. * Male participant and females of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. * Written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an Investigator or a qualified designee. Exclusion Criteria: * Presence of any febrile illness or any known or suspected acute illness on the day of immunization. * Any condition, which in the opinion of the Investigator may make the participant inappropriate for the study. * Clinically significant bleeding disorder (e.g., clotting factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following intramuscular injections or venipuncture. * Receiving systemic immunomodulatory therapy or history of receiving chemotherapy in the last 5 years other than topical agents. * Receipt of systemic glucocorticoids (a dose ≥20 mg/day prednisone or equivalent for 14 days) within 1 month, or any other cytotoxic or immunosuppressive drug within 6 months prior to injection of study vaccine. * Cancer diagnosis in the last 5 years, excluding basal cell and squamous cell carcinoma of the skin, which are allowed. * Presence of autoimmune disease. * Receipt of any investigational drug within 6 months. * Receipt of any non-COVID-19 authorized vaccines, for example influenza, within 2 weeks of receiving study dose injection. * Receipt of any other experimental SARS-CoV-2/COVID-19 or other experimental coronavirus vaccine(s) at any time prior to or during the study. Exception: Receipt of SARS CoV 2/COVID-19 vaccines at least 4 months prior to Day 0 that were experimental at the time of their administration but are currently authorized will not lead to exclusion. * Receipt of blood products or immunoglobulin (IVIg or IMIg) within 3 months of study entry/baseline serologic evaluation. * Current anti-tuberculosis therapy. * History of any reaction or hypersensitivity likely to be exacerbated by any component of the study vaccine. * Hematologic or biochemical laboratory abnormalities (blood or urine), as defined by lab normal ranges. To exclude transient abnormalities, the Investigator may repeat a test once, and if the repeat test is normal according to local reference ranges, participant may be enrolled. Abnormalities of laboratory values will not be exclusionary if considered not clinically significant by the Investigator. * Previous (within 4 months prior to Day 0) SARS-CoV-2 infection, based on a documented positive polymerase chain reaction (PCR) test or rapid antigen test, or reported by participant or prior medical history. * Member of the study personnel, or immediate family member or household member of the study personnel.