1. Had significant exposure to someone with SARS-CoV-2 infection or COVID-19 in the past 14 days, as defined by the CDC as a close contact (without PPE) of someone who has had COVID 19. 2. Participant is acutely ill or febrile (temperature = 38.0°C/100.4°F) 72 hours prior to or at the Screening Visit or Day 1. Participants meeting this criterion may be rescheduled within the 28-day screening window and will retain their initially assigned participant number. 3. Had tested positive for SARS-CoV-2 by approved/authorized lateral flow/rapid antigen or PCR test on 08 November 2021 or later. 4. Has received a COVID-19 vaccine within 3 months of the Screening Visit. 5. Has received a total of 4 doses or more of COVID-19 vaccine. 6. Has received a COVID-19 vaccine at a dose different from the authorized/approved dose. 7. History of a diagnosis or condition that, in the judgment of the Investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. Clinically unstable is defined as a diagnosis or condition requiring significant changes in management or medication within the 2 months prior to screening and includes ongoing workup of an undiagnosed illness that could lead to a new diagnosis or condition. 8. Reported history of congenital or acquired immunodeficiency, immunosuppressive condition, or immune-mediated disease requiring immunosuppressive treatment or other immunosuppressive condition. 9. Dermatologic conditions that could affect local solicited AR assessments (eg, tattoos, psoriasis patches affecting skin over the deltoid areas). 10. Reported history of anaphylaxis or severe hypersensitivity reaction after receipt of any components of mRNA vaccine. 11. Reported history of bleeding disorder that is considered a contraindication to intramuscular (IM) injection or phlebotomy. 12. Any medical, psychiatric, or occupational condition, including reported history of substance abuse, that, in the opinion of the Investigator, might pose additional risk due to participation in the study or could interfere with the interpretation of study results. Asymptomatic conditions and conditions with no evidence of end organ involvement (eg, mild hypertension, dyslipidemia) are not exclusionary, provided that they are being appropriately managed and are clinically stable (ie, unlikely to result in symptomatic illness within the time course of this study). Illnesses or conditions may be exclusionary, even if otherwise stable, due to therapies used to treat them (eg, immune modifying treatments), at the discretion of the Investigator. 13. Has received systemic immunosuppressants or immune-modifying drugs for > 14 days in total within 181 days prior to screening (for corticosteroids = 10 mg/day of prednisone equivalent) or is anticipating the need for immunosuppressive treatment at any time during participation in the study. 14. Has received or plans to receive any licensed vaccine = 28 days prior to the study injection (Day 1) or plans to receive a licensed vaccine within 28 days after the study injection (with the exception that approved seasonal influenza vaccine may be received by at least 7 and preferably 14 days apart from the stud

1. Had significant exposure to someone with SARS-CoV-2 infection or COVID-19 in the past 14 days, as defined by the CDC as a close contact (without PPE) of someone who has had COVID 19. 2. Participant is acutely ill or febrile (temperature = 38.0°C/100.4°F) 72 hours prior to or at the Screening Visit or Day 1. Participants meeting this criterion may be rescheduled within the 28-day screening window and will retain their initially assigned participant number. 3. Had tested positive for SARS-CoV-2 by approved/authorized lateral flow/rapid antigen or PCR test on 08 November 2021 or later. 4. Has received a COVID-19 vaccine within 3 months of the Screening Visit. 5. Has received a total of 4 doses or more of COVID-19 vaccine. 6. Has received a COVID-19 vaccine at a dose different from the authorized/approved dose. 7. History of a diagnosis or condition that, in the judgment of the Investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. Clinically unstable is defined as a diagnosis or condition requiring significant changes in management or medication within the 2 months prior to screening and includes ongoing workup of an undiagnosed illness that could lead to a new diagnosis or condition. 8. Reported history of congenital or acquired immunodeficiency, immunosuppressive condition, or immune-mediated disease requiring immunosuppressive treatment or other immunosuppressive condition. 9. Dermatologic conditions that could affect local solicited AR assessments (eg, tattoos, psoriasis patches affecting skin over the deltoid areas). 10. Reported history of anaphylaxis or severe hypersensitivity reaction after receipt of any components of mRNA vaccine. 11. Reported history of bleeding disorder that is considered a contraindication to intramuscular (IM) injection or phlebotomy. 12. Any medical, psychiatric, or occupational condition, including reported history of substance abuse, that, in the opinion of the Investigator, might pose additional risk due to participation in the study or could interfere with the interpretation of study results. Asymptomatic conditions and conditions with no evidence of end organ involvement (eg, mild hypertension, dyslipidemia) are not exclusionary, provided that they are being appropriately managed and are clinically stable (ie, unlikely to result in symptomatic illness within the time course of this study). Illnesses or conditions may be exclusionary, even if otherwise stable, due to therapies used to treat them (eg, immune modifying treatments), at the discretion of the Investigator. 13. Has received systemic immunosuppressants or immune-modifying drugs for > 14 days in total within 181 days prior to screening (for corticosteroids = 10 mg/day of prednisone equivalent) or is anticipating the need for immunosuppressive treatment at any time during participation in the study. 14. Has received or plans to receive any licensed vaccine = 28 days prior to the study injection (Day 1) or plans to receive a licensed vaccine within 28 days after the study injection (with the exception that approved seasonal influenza vaccine may be received by at least 7 and preferably 14 days apart from the stud