Factor Xa Inhibitor Versus Standard of Care Heparin in Hospitalized Patients With COVID-19 (XACT)

Inclusion Criteria: * Patients age 18-100 admitted to hospital with laboratory-confirmed SARS-CoV-2 infection * Not be intubated or mechanically ventilated or imminently at risk for same or ICU admission within 24 hours of enrollment. * Not be admitted for central nervous system (CNS) diagnosis * Not have a current history of a condition requiring full therapeutic anticoagulation such as venous thromboembolism, atrial fibrillation. Exclusion Criteria: Medical Conditions * Life expectancy of less than 6 months * Active or recent gastrointestinal bleeding in the past 6 months * Intracranial bleeding in the past 6 months * Major trauma or head trauma in the past 2 months * Major surgery in the past 2 months or planned within 2 weeks after completion of the study * Recent spinal or epidural procedures in the past 2 weeks * Ischemic stroke in the past 2 weeks * History of intracranial neoplasm, arteriovenous malformation or aneurysm * History of acquired or spontaneous impairment of hemostasis such as but not limited to hemophilia, idiopathic thrombocytopenic purpura (ITP), thrombotic thrombocytopenic purpura (TTP), von Willebrand disease * Allergy to heparin or rivaroxaban or any factor Xa inhibitors, including a history of heparin-induced thrombocytopenia * History of antiphospholipid syndrome * End-stage renal failure requiring dialysis * Valvular heart disease requiring chronic anticoagulation * History of atrial fibrillation, atrial flutter or venous thromboembolic event (VTE) currently requiring anticoagulation * History of solid organ transplant requiring immunosuppressant therapy * Cancer requiring ongoing anticoagulation * History of cirrhosis or liver failure, hepatorenal syndrome * History of baseline bronchiectasis * History of systemic lupus erythematosus or other autoimmune diseases requiring immunosuppressant therapy. Vital signs * Uncontrolled hypertension: systolic blood pressure (SBP) \> 180 mm Hg or diastolic blood pressure (DBP) \> 105mm Hg. Subjects who have a transient, higher blood pressure elevation (SBP 180-200 mm Hg) may enter the study if a repeat confirmation is back in range prior to enrollment. Laboratory * PT INR \> 2.0. * Platelet \< 90 10\^3/µL * Total bilirubin \> 3.0 mg/dL * Hemoglobin \< 9.0 g/dL * Urine with gross hematuria (not due to menses) * Estimated glomerular filtration rate (GFR) less than 30 mL/min calculated with the Cockcroft-Gault formula Medications * Patients on dual anti-platelet therapy * Patients taking hypoxia-inducible factor prolyl hydroxylase inhibitors (such as roxadustat.) * Erythropoiesis-stimulating agents (such as epoetin alfa, darbepoetin alfa) Other COVID-19 drug studies or trials * Any COVID19 vaccination trials * Experimental COVID drug trial except for treatment(s) that has become accepted standard of care.