To evaluate the efficacy of ADG20 compared to placebo in the treatment of mild or moderate COVID-19 in participants at high risk of disease progression. Hospitalization is defined as ≥24 hours of acute care in a hospital or acute care facility (includes emergency rooms, intensive care units, acute care facilities created for COVID-19 pandemic hospitalization needs, or other acute care facilities). All-cause death is defined as death for any reason from Day 1 (postdose) through Day 29.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to Whole Genome WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Proportion of participants with at least one treatment emergent AE

Safety Set: All participants who received any amount of study drug. Participants were analyzed based on the actual treatment (ADG20 versus Placebo) received. Participants with more than one AE were only counted once.

Proportion of participants with at least one solicited injection site reaction

Safety Set: All participants who received any amount of study drug. Participants were analyzed based on the actual treatment (ADG20 versus Placebo) received.

Proportion of participants with a potentially clinically significant change from baseline in post-baseline laboratory parameters - data presented for any analyte with >/= 2% in any arm

Safety Set: All participants who received any amount of study drug. Participants were analyzed based on the actual treatment (ADG20 versus Placebo) received.

Participants with Potentially Clinically Significant Changes (PCS) From Baseline in Vital Signs (Body Temperature, Heart Rate, Respiration Rate, and Systolic and Diastolic Blood Pressure) at Any Time Post-Baseline

Safety Set: All participants who received any amount of study drug. Participants were analyzed based on the actual treatment (ADG20 versus Placebo) received.

Proportion of participants with COVID-19-related medically attended visit (telemedicine, physician office, urgent care center, emergency room, hospitalization) or all-cause death through Day 29. In addition to events defined as the primary efficacy endpoint, this endpoint also includes any medically attended visits, in-person, or telemedicine, not specified in the protocol. These include unscheduled in-person or telemedicine visits conducted by the investigator for the purpose of evaluating worsening signs or symptoms attributed to COVID-19 or emergency room, urgent care center or physician office visits, or hospitalization for attention to worsening signs or symptoms attributed to COVID-19, in the opinion of the investigator. Incidence of COVID-19-related medically attended visits or all-cause death includes participants who met any event defined for this endpoint. Participants were counted only once even if multiple events were met in the time frame.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Proportion of participants with any COVID 19-related emergency room visits, COVID-19-related hospitalization, or all cause death through Day 29. Defined as any stay in a hospital or acute care facility regardless of duration (includes emergency rooms, intensive care units, acute care facilities created for COVID-19 pandemic hospitalization needs, or other acute care facilities) for attention to worsening signs or symptoms attributed to COVID-19 in the opinion of the investigator or all cause death through Day 29. Incidence of COVID-19-related emergency room visits, COVID-19-related hospitalization, or all-cause death includes participants who met any event defined for this endpoint. Participants were counted only once even if multiple events were met in the time frame.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to WGS-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Proportion of participants with Severe/Critical COVID-19 or all-cause death through Day 29. All-cause death is defined as death for any reason (from Day 1postdose) through Day 29. Severity is based on the investigator's assessment of severity (eCRF COVID-19 Severity Assessment) per the protocol definitions. Incidence of Severe/Critical COVID-19 or all-cause death includes participants who met any event defined for this endpoint. Participants were counted only once even if multiple events were met in the time frame.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Time to sustained recovery (improvement or resolution) of COVID-19 symptoms through Day 29: Defined as the time from the first dose date to the earliest date when sustained improvement or sustained resolution of COVID-19 symptoms is met (as detailed below) through Day 29. COVID-19 symptoms assessed include fever, chills, cough, sore throat, congestion, shortness of breath/difficulty breathing at rest, shortness of breath/difficulty breathing with exertion, muscle or body aches, fatigue, headache, nausea, vomiting, and diarrhea. Loss of taste/smell is excluded from this analysis.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Defined as death for any reason from Day 1 (postdose). In the overall survival analysis, participants who are alive or lost to follow-up at the time of analysis are censored at the date of last contact.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Time to sustained resolution of COVID-19 symptoms through Day 29: Defined as time from the dose date to the first date when all of the defined symptoms are scored as absent with no symptom recurrence or new symptoms, except cough, fatigue, and headache which may be mild or absent, through Day 29.

Modified Full Analysis Set (mFAS-non-Omicron): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants.

Assessed by RT qPCR From NP (Nasopharyngeal) Samples

Modified Full Analysis Set (mFAS-non-Omicron-NP): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants with a positive baseline NP sample.

Duration of SARS-CoV-2 viral shedding is defined as time from the dose date to the first date the viral load is not detected, ie, below the limit of detection (LOD), and sustained through Day 29. Participants who do not have the defined event or who discontinue study prior to Day 29 are censored at the earlier date of the last viral load assessment or Day 30. Deaths occurring prior to Day 29 were censored at Day 30.

Modified Full Analysis Set (mFAS-non-Omicron-S): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants with a positive baseline saliva sample.

Proportion of participants with Viral load >5 (log10 copies/mL) on Day 7 assessed by RT-qPCR from NP sample.

Modified Full Analysis Set (mFAS-non-Omicron-NP): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants with a positive baseline NP sample.

Proportions of SARS-CoV-2 viral clearance (Days 3, 5, 7, 11, 14, 21, and 29) assessed by RT-qPCR from saliva samples: In the mFAS-S, the cumulative proportion of participants with viral clearance (viral load not detected and sustained through Day 29) at Days 3, 5, 7, 11, 14, 21, and 29 will be assessed by RT-qPCR from saliva samples. Participants who have died or discontinued study prior to Day 29 are assumed to have no viral clearance.

Modified Full Analysis Set (mFAS-non-Omicron-S): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants with a positive baseline saliva sample.

The AUC from Day 1 through Day 29 was calculated according to the linear trapezoidal rule using the measured SARS-CoV-2 viral load above the lower limit of quantification. No AUC values will be calculated when Day 1 and/or Day 29 values are missing, or if there are more than 3 values missing in the profile.

Modified Full Analysis Set (mFAS-non-Omicron-S): All randomized participants with COVID-19 due to Whole Genome Sequencing (WGS)-confirmed or suspected non-Omicron SARS-CoV-2 variants with a positive baseline saliva sample.

An AE is defined as any untoward medical occurrence in a participant enrolled into this study regardless of its causal relationship to the study drug. AEs occurring from when the participant signed the ICF until the Month 14 (EOS) visit or discontinuation from study was recorded

Percent of participants who reported at least one TEAE.

A PCS value is defined as any DAIDS grade 4 post-baseline or any increase of 2 or more DAIDS grades post-baseline, except for PCS low creatinine clearance, which is defined as any DAIDS Grade 4 post-baseline or any DAIDS grade shift from 0 to 3. Laboratory parameters not graded by DAIDs will be defined as PCS based on the criteria in the SAP (Appendix K.)

Safety Set: All participants who received any amount of study drug. Participants were analyzed based on the actual treatment (ADG20 versus Placebo) received. Data presented for any analyte with >/= 2% in any arm.

Safety Set: All participants who received any amount of study drug. Participants were analyzed based on the actual treatment (ADG20 versus Placebo) received.

All participants in the Safety Set who had a valid immunogenicity test result before the dose of study drug, and at least 1 valid result after the dose of study drug; analysis limited to participants who received ADG20 only.

Post-baseline Treatment-emergent Variations at Amino Acid Positions Associated with Reduced Susceptibility to ADG20 (>/= 15% Allele frequency); data limited to mutations observed.

Participants with any mutation at a monitored position >/= 15% allele frequency, in the population that had a qualifying (passed QC testing) baseline and post-baseline Whole Genome Sequencing sample.