Key Inclusion Criteria:

1. Hospitalization for COVID-19 infection
2. Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 infection confirmed by polymerase chain reaction (PCR)
3. Participant requires supplemental oxygen for pulmonary distress related to COVID-19 infection, and has been on supplemental oxygen for no more than 96 hours from time of screening

Key Exclusion Criteria:

1. Malabsorption syndrome, disease significantly affecting gastrointestinal function, or resection of the stomach or small bowel, symptomatic inflammatory bowel disease or ulcerative colitis, or partial or complete bowel obstruction
2. On a Bruton's tyrosine kinase (BTK) inhibitor
3. Planned or concurrent use of a host modifiers/immune-based therapies or anti-CD20 monoclonal antibody treatment
4. Participants with prior of current hematologic malignancy or solid tumor malignancy with treatment within 6 months prior to study entry

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.