Acalabrutinib Study With Best Supportive Care in Participants Hospitalized With COVID-19

Inclusion Criteria: 1. Participant or legally authorized representative must be able to understand the purpose and risks of the study and provide written informed consent and authorization to use protected health information (in accordance with national and local patient privacy regulations). 2. Participants who are hospitalized with coronavirus (SARS-CoV-2) infection, confirmed by PCR test or other commercial or public health assay in any specimen, as documented by either of the following: 1. PCR positive in sample collected \< 72 hours prior to first dose, OR 2. PCR positive in sample collected ≥ 72 hours prior to first dose (but no more than 14 days prior to first dose), documented inability to obtain a repeat sample (eg, due to lack of testing supplies, limited testing capacity, results taking \> 24 hours, etc), AND progressive disease suggestive of ongoing SARS-CoV-2 infection 3 Evidence of respiratory failure attributable to COVID-19 pneumonia (documented radiographically) before enrollment 4 Nasogastric tube or other types of oral or percutaneous gastric feeding tube; placement must be radiographically confirmed and expected to remain in place, as judged by the investigator, for a minimum of 3 days after study enrolment. 5 Has received treatment with PPIs (eg, omeprazole, esomeprazole, lansoprazole, dexlansoprazole, rabeprazole, or pantoprazole) for a minimum of 24 hours immediately prior to enrollment; any PPI will be permitted, provided it meets the minimum equivalent daily dose of 20 mg rabeprazole. Exclusion Criteria: 1. Any serious and uncorrectable medical condition or abnormality of clinical laboratory tests that, in the Investigator's judgment, precludes the participant's safe participation in and completion of the study. 2. In the opinion of the Investigator, progression to death is imminent and inevitable within the next 24 hours, irrespective of the provision of treatments. 3. Current refractory nausea and vomiting, malabsorption syndrome, disease significantly affecting gastrointestinal function, resection of the stomach, extensive small bowel resection that is likely to affect absorption, symptomatic inflammatory bowel disease, partial or complete bowel obstruction, or gastric restrictions and bariatric surgery, such as gastric bypass. 4. Received BTK inhibitor within 7 days before enrollment. 5. Requires or is receiving anticoagulation with warfarin or equivalent vitamin K antagonists (eg, phenprocoumon) within 7 days prior to enrollment. Other anticoagulants are permitted. 6. Participants on dual antiplatelet and therapeutic anticoagulant therapy (eg, aspirin and therapeutic doses of low molecular weight heparin are not allowed; however, aspirin and prophylactic/ low doses of low-molecular-weight heprin are allowed).