Ascending Dose Study of Investigational SARS-CoV-2 Vaccine ARCT-021 in Healthy Adult Subjects

Inclusion Criteria: 1. Healthy males or females aged 21 to 80 at the time of informed consent. 2. Body Mass Index 18-35 kg/m2, inclusive, at screening 3. Willing to refrain from strenuous exercise/activity (for example heavy lifting, weight training, intense aerobics classes etc.) and alcohol for at least 72 hours prior to study visits 4. Temperature is less than 99.3 degrees Fahrenheit (37.4 degrees Celsius) at screening AND at the pre-dose evaluation on Day 1 5. Willing and able to comply with protocol-defined procedures and complete all study visits 6. Males must be surgically sterile or willing to use adequate contraception; females must be post-menopausal, surgically sterile or willing to use adequate contraception Exclusion Criteria: 1. Pregnant or breast feeding 2. Clinically significant abnormalities in medical history 3. Out of range screening laboratory results 4. Known history of or positive test for human immunodeficiency virus (HIV), hepatitis C or chronic hepatitis B 5. Uncontrolled hypertension (BP \> 160/100 mm Hg) 6. Uncontrolled diabetes 7. Any history of autoimmune disease 8. Immunodeficiency of any cause 9. History of Chronic liver disease 10. Treatment with another investigational drug, biological agent, or device within one month of screening, or 5 half-lives of investigational drug, whichever is longer 11. Recent (within 1 year) history of, or current drug or alcohol abuse 12. Has any blood dyscrasias or significant disorder of coagulation 13. Has an acute illness, as determined by the investigator, with or without fever \[temperature \>38.0 degrees Celsius (100.4 degrees Fahrenheit)\] within 72 hours prior to each vaccination 14. Malignancy within 5 years, except for basal or squamous cell carcinoma of the skin or carcinoma in situ of the cervix that has been successfully treated. 15. Received or plans to receive another vaccine within 4 weeks before study vaccination or at any time during the study. 16. Receipt of any other SARS CoV-2 or other experimental coronavirus vaccine at any time prior to study or planned during the study 17. Have any other conditions, which, in the opinion of the Investigator or Sponsor would make the subject unsuitable for inclusion, or could interfere with the subject participating in or completing the Study