1. a) Receipt of vaccines or medications or vaccines intended to prevent or treat COVID-19 in the past year. b) Prior receipt of any investigational COVID-19 vaccine, or other investigational or non-registered medicinal product (study drug, biologic, or device) within the past year. 2. Currently enrolled or plan to participate in another clinical trial with an investigational agent (including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication) to be received during the study period. 3. Older adult subjects meeting frail elderly criteria (older persons with medical, nutritional, cognitive, emotional, or activity impairments, as defined by the study site), acute or progressive, unstable or uncontrolled clinical conditions. 4. Acute or chronic progressive, unstable or uncontrolled clinical conditions, 5. For all subjects: Receipt of licensed inactivated vaccines including influenza vaccine within 14 days prior to study vaccine administration on Study Day 0, or with live virus vaccines within 30 days of Study Day 0. 6. History of hypersensitivity or serious adverse reactions to vaccines, such as anaphylaxis, Guillain-Barré, and angioedema, or any known allergies to any component of the IVX-411 vaccine, or hypersensitivity to latex. 7. Abnormal function of the immune system resulting from clinical conditions including human immunodeficiency virus, chronic administration of systemic corticosteroids or administration of immunosuppressive chemotherapy, biologics, or radiotherapy within the past 3 months before study randomization. 8. Positive for human immunodeficiency virus (HIV), hepatitis B surface antigen (HBsAg), and hepatitis C virus (HCV) antibody. 9. Receipt of immunoglobulins or any blood products within the past 3 months before study randomization. 10. BMI greater than 35 kg/m2 at screening. 11. Positive pregnancy test at screening. 12. Refusal to maintain contraceptive practices during the study, and (for women of childbearing potential) to be screened for pregnancy for the duration of the study.

1. a) Receipt of vaccines or medications or vaccines intended to prevent or treat COVID-19 in the past year. b) Prior receipt of any investigational COVID-19 vaccine, or other investigational or non-registered medicinal product (study drug, biologic, or device) within the past year. 2. Currently enrolled or plan to participate in another clinical trial with an investigational agent (including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication) to be received during the study period. 3. Older adult subjects meeting frail elderly criteria (older persons with medical, nutritional, cognitive, emotional, or activity impairments, as defined by the study site), acute or progressive, unstable or uncontrolled clinical conditions. 4. Acute or chronic progressive, unstable or uncontrolled clinical conditions, 5. For all subjects: Receipt of licensed inactivated vaccines including influenza vaccine within 14 days prior to study vaccine administration on Study Day 0, or with live virus vaccines within 30 days of Study Day 0. 6. History of hypersensitivity or serious adverse reactions to vaccines, such as anaphylaxis, Guillain-Barré, and angioedema, or any known allergies to any component of the IVX-411 vaccine, or hypersensitivity to latex. 7. Abnormal function of the immune system resulting from clinical conditions including human immunodeficiency virus, chronic administration of systemic corticosteroids or administration of immunosuppressive chemotherapy, biologics, or radiotherapy within the past 3 months before study randomization. 8. Positive for human immunodeficiency virus (HIV), hepatitis B surface antigen (HBsAg), and hepatitis C virus (HCV) antibody. 9. Receipt of immunoglobulins or any blood products within the past 3 months before study randomization. 10. BMI greater than 35 kg/m2 at screening. 11. Positive pregnancy test at screening. 12. Refusal to maintain contraceptive practices during the study, and (for women of childbearing potential) to be screened for pregnancy for the duration of the study.