Safety and Immunogenicity Study of a Booster Dose of the Investigational CV0501 mRNA COVID-19 Vaccine in Adults at Least 18 Years Old

Inclusion Criteria: 1. Must provide documented informed consent prior to any study procedures being performed 2. Is capable of understanding and agrees to comply with planned study procedures and to be available for all study visits 3. Has received at least 2 doses of Comirnaty or Moderna COVID-19 Vaccine (Spikevax®\\), with the last dose of vaccine received at least 6 months prior to screening 4. Negative for SARS-CoV-2 infection by RT-PCR test at screening 5. Is a male or nonpregnant female \>= 18 years old 6. If the participant is a woman of childbearing potential, the participant agrees to use at least 1 highly effective form of contraception for at least 30 days prior to the study vaccination up to 3 months after study vaccination. 7. Agrees to refrain from blood or plasma donation from the first study vaccination through end of study. 8. Has a body mass index of 18 to 40 kg/m\^2, inclusive, at screening. 9. Is healthy or medically stable as determined by investigator judgment based on medical history, clinical laboratory tests, vital sign measurements, and physical examination findings Exclusion Criteria: 1. Participant is female and has a positive pregnancy test result at screening. 2. Participant is female and is breastfeeding or will (re)start breastfeeding from the study vaccination to 3 months after vaccination. 3. Has an acute febrile illness with temperature \>=38.0°C or \>=100.4°F within 72 hours before study vaccination. Individuals with suspected COVID-19 symptoms should be excluded and referred for medical care. 4. Has a history of documented SARS-CoV-2 infection or COVID-19 within 6 months before screening. 5. Has a documented medical history of HIV, hepatitis B or hepatitis C infection prior to screening, or a positive test for these conditions at screening. 6. Any confirmed or suspected immunosuppressive or immunodeficient condition resulting from disease (eg, malignancy) or immunosuppressive/cytotoxic therapy (eg, medications used during cancer chemotherapy, organ transplantation or to treat autoimmune disorders). Chronic use (more than 14 continuous days) of any medication that may be associated with changes in immune function including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy immunotherapy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs within 6 months of the first study vaccination. Inclusion of persons who use low dose topical, ophthalmic, inhaled, or intranasal steroid preparations is permitted. 7. History of myocarditis, pericarditis, or idiopathic cardiomyopathy, or presence of any medical condition that increases risk of myocarditis or pericarditis, including cocaine abuse, cardiomyopathy, endomyocardial fibrosis, hypereosinophilic syndrome, hypersensitivity myocarditis, eosinophilic granulomatosis with polyangiitis, persistent myocardial viral infection (eg, due to enterovirus or adenovirus), and celiac disease. 8. Has a new onset, clinically significant, abnormal biochemistry or hematology finding (defined as \>= Grade 1) at screening (adults with Grade 1 laboratory abnormalities that have been stable for at least 6 months before enrollment may be included in the study). 9. Individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to: systemic or cutaneous lupus erythematosus, autoimmune arthritis/rheumatoid arthritis, Guillain- Barré syndrome, multiple sclerosis, Sjögren's syndrome, idiopathic thrombocytopenia purpura, glomerulonephritis, autoimmune thyroiditis, giant cell arteritis (temporal arteritis), Takayasu arteritis, granulomatosis with polyangiitis, psoriasis, and insulin-dependent diabetes mellitus (Type 1). 10. Has an unstable chronic medical condition. This refers to a condition requiring a new medication or increase in dose of current medication(s) or a condition requiring hospitalization within 6 months prior to screening. 11. Has a history of hypersensitivity or severe allergic reaction, including anaphylaxis, generalized urticaria, angioedema, and other significant reactions, to vaccines or to any component of the investigational product. 12. Has received or plans to receive any licensed vaccine, within 4 weeks before or 4 weeks after study vaccination. Inactivated vaccines for influenza are permitted during the study if they are administered at least 14 days before or after study vaccination. 13. Has had known close contact with anyone who had a confirmed SARS-CoV-2 infection within 2 weeks before study vaccination. Rescreening of these participants permitted after quarantine period is complete. 14. Has participated or plans to participate in another investigational study involving any investigational product or device within 6 months or 5 half-lives, whichever is longer, before the study vaccination through end of study. 15. Has received or plans to receive immunoglobulins or any blood or blood products within 3 months before the first study vaccination through end of study. 16. Has a bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 17. Has a history of alcohol abuse or other recreational drug use (excluding cannabis) within 6 months before study vaccination. 18. Has any abnormal skin condition or permanent body art (eg, tattoo) that would interfere with the ability to observe local reactions at the injection site. 19. Has a medical disease or psychiatric condition that, in the opinion of the investigator, precludes study participation because it would place the individual at an unacceptable risk of injury, render the individual unable to meet the requirements of the protocol or interfere with the individual's successful completion of the trial. 20. Participant is an employee or family member of the investigator or study site personnel.