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.

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.

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.

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.