This first-in-human study is designed to evaluate the safety, tolerability, pharmacokinetics, anti-drug antibodies, and neutralizing activity of MDX2301 administered by intravenous (IV), intramuscular (IM), or subcutaneous (SC) routes in healthy adults and adults at higher risk for severe COVID-19. Participants will receive single IV, IM, and SC doses of MDX2301 or placebo and a repeat IM or SC dose approximately 3 months apart of MDX2301 or placebo.

Inclusion Criteria

Healthy Adults

1. Participant is a healthy male or female, 18 to 64 years of age.

2. Participant is in good health in the opinion of the investigator.

   Adults at Higher Risk for Developing Severe COVID-19:

3. Participant is a male or female, 18 to 64 years of age.

4. Participant is at higher risk for developing severe COVID-19, with 1 or more of the following risk factors:

   1. Asthma
   2. Diabetes
   3. Cerebrovascular disease, which affects blood flow to the brain.
   4. Chronic kidney disease
   5. Chronic lung disease
   6. Cardiac disease
   7. Chronic liver disease
   8. Cystic fibrosis
   9. HIV clinically stable on antiretroviral therapy for at least 6 months prior to screening.
   10. Sickle cell disease or thalassemia

5. Participant is clinically stable with no clinically significant abnormalities.

6. Participant has not been hospitalized within the 12 months prior to screening or is not expected to be hospitalized during the study due to underlying medical conditions.

   All Participants

7. Female participants of childbearing potential must have a negative urine pregnancy test.

8. Female participants of childbearing potential must agree to follow instructions for a highly effective birth control method.

9. Participant is able to understand and sign the informed consent form prior to undergoing any study procedures.

10. Participant is willing and able to comply with scheduled visits and procedures.

Exclusion Criteria:

Healthy Adults

1. Participant has any chronic or significant medical condition that, in the opinion of the investigator, might compromise the participant's safety or interfere with evaluation of the study drug.

2. Participant has evidence of active HIV, hepatitis B, or hepatitis C infections at screening.

   Adults at Higher Risk for Severe COVID-19:

3. Participant has any serious disease, condition, or disorder that, in the opinion of the investigator, might compromise the participant's safety or interfere with evaluation of the study drug or interpretation of study results, or may lead to hospitalization or death within the study period.

4. Participant has evidence of active hepatitis B or hepatitis C infections at screening.

   All Participants

5. Participant has abnormal vital signs, ECG findings, or laboratory values at Screening or Day -1.

6. Participant tests positive for SARS-CoV-2 infection at screening.

7. Participant self-reports having COVID-19 or received COVID-19 antiviral for prophylaxis or treatment prior to Day 1.

8. Participant has received a SARS-CoV-2 vaccine prior to dosing.

9. Participant has received a monoclonal antibody (mAb) for SARS-CoV-2 or convalescent plasma for SARS-CoV-2 prior to Day 1.

10. Participant has received or is expected to receive for the duration of the study immunoglobulin, blood-derived products, high-dose systemic corticosteroids, or other immunosuppressant drugs within 6 months prior to Day 1.

11. Participant is pregnant, breastfeeding, or seeking pregnancy while on the study.

12. Participant with a known clinically significant bleeding disorder that would prohibit the participant from receiving an IV infusion or IM or SC injection.

13. Participant had major surgery within 30 days prior to Day 1.

14. Participant has donated blood prior to screening.

15. Participant has any skin condition and/or tattoo that may interfere with the evaluation of safety at the injection site.

16. Participant has a history of alcoholism or illicit drug use prior to screening or a positive test for drugs of abuse at screening or on Day -1.

17. Participant is a current smoker or user of other nicotine containing products on a daily basis.

18. Participant has received an investigational product within 30 days prior to Day 1.

19. Participant has a known hypersensitivity to any components of MDX2301, any of its excipients or closely related compounds.

    For All Participants, Temporary Exclusions for Randomization on Day 1 if Remains within the Screening Window:

20. Participant has any acute illness, within 3 days of Day 1.

21. Participant has vital signs considered by the investigator to be clinically significant prior to study drug administration.

22. Participant has had close contact with anyone confirmed to have SARS-CoV-2 infection within the 7 days prior to Day 1.

23. Any acute drug therapy prescribed by a physician within 7 days prior to Day 1.

Sponsor staff will remain blinded until two administrative looks are conducted in order to facilitate future study planning.