The primary objective of the study is to evaluate the safety and tolerability of REGN14284 in healthy participants, as measured by all treatment-emergent adverse events (TEAEs) and treatment-emergent serious adverse events (SAEs).

The secondary objectives of the study are:

• To assess the concentration-time profile of REGN14284 in serum
• To assess the immunogenicity of REGN14284

Key Inclusion Criteria:

1. Has SARS-CoV-2-negative test result from a sample collected ≤72 hours prior to randomization as described in the protocol.
2. Has received complete primary series of standard-of-care COVID-19 vaccination per local guidance, completed at least 2 weeks prior to screening
3. Has a body mass index (BMI) between 18 and 31 kg/m2 (inclusive) at the screening visit
4. Is judged by the investigator to be in good health based on medical history, physical examination, vital sign measurements, laboratory safety testing and ECGs performed at screening and/or prior to administration of study drug

Key Exclusion Criteria:

1. History of clinically significant cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrine, hematological, infectious, autoimmune, oncologic, psychiatric or neurological disease, as assessed by the investigator as described in the protocol
2. Presents any concern to the investigator that might confound the results of the study or poses an additional risk to the participant by their participation in the study
3. Was hospitalized (ie, >24 hours) for any reason within 30 days of the screening visit
4. Has a history of alcohol or drug abuse as determined by the investigator
5. Has a history of significant multiple and/or severe allergies, or has had an anaphylactic reaction to drugs or food as described in the protocol
6. Use of any medications or nutritional supplements within approximately 5 half-lives or 2 weeks, whichever is longer, prior to first administration of the study drug through the end of the study, except for the permitted medications listed as described in the protocol
7. Participated in any clinical research study evaluating another investigational drug including biologics or specific immunotherapy, within at least 5 half-lives or 90 days (whichever is longer) of an investigational biologic drug, or at least 4 weeks for small molecules or other investigational drugs, prior to the screening visit

NOTE: Other protocol defined inclusion / exclusion criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing

When Regeneron has received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication, has made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry), has the legal authority to share the data, and has ensured the ability to protect participant privacy.

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf