Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Lung failure is the main cause of death related to COVID-19 infection. The main objective of this study is to evaluate the safety and tolerability of ABBV-47D11 and ABBV-2B04 given alone and in combination to participants with COVID-19 infection. In addition, this study will evaluate the pharmacokinetics (how the body handles the study drug) and anti-viral activity of the study drug.

ABBV-47D11 and ABBV-2B04 are investigational anti-SARS-CoV-2 monoclonal antibodies being developed for the treatment of COVID-19. Study will be conducted in two parts. In part A, participants will receive ABBV-47D11 or placebo. There is a 1 in 4 chance that participants will be assigned to placebo. In part B, participants will receive ABBV-2B04 alone or in combination with ABBV-47D11 or placebo. There is a 1 in 5 chance that participants will be assigned to placebo. Around 54 adult participants with COVID-19 will be enrolled in approximately 10 to 30 sites globally.

In part A participants will receive single intravenous (into the veins) infusion of ABBV-47D11 or placebo on Day 1. In part B participants will receive single intravenous (into the veins) infusion of ABBV-2B04 alone or in combination with ABBV-47D11 or placebo on Day 1. Participants will be followed up for 106 days.

There may be higher treatment burden for participants in this trial compared to their standard of care. The effect of the treatment will be checked by medical assessments, blood tests, nasal swabs and presence of side effects.

Part B of this study was not conducted.

Inclusion Criteria:

• Confirmed SARS-CoV-2 infection based on initial nucleic acid or antigen testing from respiratory swab, saliva, or other bodily fluid within 7 days prior to randomization.
• Must have >= 1 symptom associated with COVID-19 with an onset of <= 8 days prior to randomization.
• Hospitalized or plans for hospital admission due to COVID-19 at the time of randomization or not currently hospitalized and does not have plans for hospital admission at the time of randomization, but is willing to be confined for ≥ 48 hours post-dose for the purposes of participating in this research study

Exclusion Criteria:

• Have an oxygen saturation (SpO2) < 88% on room air at rest for 5 minutes OR ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) <= 200 mmHg at randomization.
• Requiring high-flow nasal cannula oxygen therapy/non-invasive or invasive mechanical ventilation/extracorporeal membrane oxygenation (ECMO) or anticipated impending need for high-flow nasal cannula oxygen therapy/non-invasive or invasive mechanical ventilation/ECMO.
• Prior treatment with a SARS-CoV-2 specific monoclonal antibody or convalescent COVID-19 plasma.