• 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.

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.