1. severe or critical covid-19, e.g.: * respiratory rate ≥ 30 breaths per minute or * heart rate ≥ 125 beats per minute or * respiratory failure, defined as clinical need for high-flow oxygen therapy, non- invasive positive pressure ventilation or endotracheal intubation and mechanical ventilation or * shock, defined as systolic blood pressure \<90 mm hg or diastolic blood pressure \<60 mm hg or requiring vasopressors or * multi-organ dysfunction/failure (who clinical progression scale score ≥6) 2. hospitalisation for reasons other than severity of covid-19 or comorbidities (e.g. social reasons, local policies, isolation/quarantine). 3. active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer). 4. history of significant haemorrhage (requiring hospitalisation or transfusion) outside of a surgical setting within the last 24 months. 5. familial bleeding diathesis. 6. glucose-6-phosphate dehydrogenase deficiency. 7. severe hepatic and renal impairment as no safety and pk data of isoquercetin are available in these populations. 8. current daily use of aspirin (\> 81 mg daily), clopidogrel (plavix), cilostazol (pletal), aspirin-dipyridamole (aggrenox) (within 10 days) or considered to use regular use of higher doses of non-steroidal anti-inflammatory agents as determined by the treating physician (e.g. ibuprofen \> 800 mg daily or equivalent). 9. concomitant use of cyclosporine, warfarin (coumarin), tpa, strong inducer of cyp3a4, or substrate of cyp3a4 with narrow therapeutic index. 10. history of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. 11. pregnancy. 12. because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. these potential risks may also apply to other agents used in this study. 13. known hypersensitivity to isoquercetin, quercetin, or to any of the excipients used in the isoquercetin capsules. 14. patient with history of poor compliance, or current or past psychiatric disease that might interfere with the ability to comply with the study procedures or give informed consent according to the judgment of the investigator or institutionalized by court decision. 15. patient with any condition that the physician judges could be detrimental to patient participating in this study.

1. severe or critical covid-19, e.g.: * respiratory rate ≥ 30 breaths per minute or * heart rate ≥ 125 beats per minute or * respiratory failure, defined as clinical need for high-flow oxygen therapy, non- invasive positive pressure ventilation or endotracheal intubation and mechanical ventilation or * shock, defined as systolic blood pressure \<90 mm hg or diastolic blood pressure \<60 mm hg or requiring vasopressors or * multi-organ dysfunction/failure (who clinical progression scale score ≥6) 2. hospitalisation for reasons other than severity of covid-19 or comorbidities (e.g. social reasons, local policies, isolation/quarantine). 3. active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer). 4. history of significant haemorrhage (requiring hospitalisation or transfusion) outside of a surgical setting within the last 24 months. 5. familial bleeding diathesis. 6. glucose-6-phosphate dehydrogenase deficiency. 7. severe hepatic and renal impairment as no safety and pk data of isoquercetin are available in these populations. 8. current daily use of aspirin (\> 81 mg daily), clopidogrel (plavix), cilostazol (pletal), aspirin-dipyridamole (aggrenox) (within 10 days) or considered to use regular use of higher doses of non-steroidal anti-inflammatory agents as determined by the treating physician (e.g. ibuprofen \> 800 mg daily or equivalent). 9. concomitant use of cyclosporine, warfarin (coumarin), tpa, strong inducer of cyp3a4, or substrate of cyp3a4 with narrow therapeutic index. 10. history of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. 11. pregnancy. 12. because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. these potential risks may also apply to other agents used in this study. 13. known hypersensitivity to isoquercetin, quercetin, or to any of the excipients used in the isoquercetin capsules. 14. patient with history of poor compliance, or current or past psychiatric disease that might interfere with the ability to comply with the study procedures or give informed consent according to the judgment of the investigator or institutionalized by court decision. 15. patient with any condition that the physician judges could be detrimental to patient participating in this study.

severe or critical covid-19, e.g.: respiratory rate ≥ 30 breaths per minute or heart rate ≥ 125 beats per minute or respiratory failure, defined as clinical need for high-flow oxygen therapy, non- invasive positive pressure ventilation or endotracheal intubation and mechanical ventilation or shock, defined as systolic blood pressure <90 mm hg or diastolic blood pressure <60 mm hg or requiring vasopressors or multi-organ dysfunction/failure (who clinical progression scale score ≥6) hospitalisation for reasons other than severity of covid-19 or comorbidities (e.g. social reasons, local policies, isolation/quarantine). active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer). history of significant haemorrhage (requiring hospitalisation or transfusion) outside of a surgical setting within the last 24 months. familial bleeding diathesis. glucose-6-phosphate dehydrogenase deficiency. severe hepatic and renal impairment as no safety and pk data of isoquercetin are available in these populations. current daily use of aspirin (> 81 mg daily), clopidogrel (plavix), cilostazol (pletal), aspirin-dipyridamole (aggrenox) (within 10 days) or considered to use regular use of higher doses of non-steroidal anti-inflammatory agents as determined by the treating physician (e.g. ibuprofen > 800 mg daily or equivalent). concomitant use of cyclosporine, warfarin (coumarin), tpa, strong inducer of cyp3a4, or substrate of cyp3a4 with narrow therapeutic index. history of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. pregnancy. because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. these potential risks may also apply to other agents used in this study. known hypersensitivity to isoquercetin, quercetin, or to any of the excipients used in the isoquercetin capsules. patient with history of poor compliance, or current or past psychiatric disease that might interfere with the ability to comply with the study procedures or give informed consent according to the judgment of the investigator or institutionalized by court decision. patient with any condition that the physician judges could be detrimental to patient participating in this study.

severe or critical covid-19, e.g.: respiratory rate ≥ 30 breaths per minute or heart rate ≥ 125 beats per minute or respiratory failure, defined as clinical need for high-flow oxygen therapy, non- invasive positive pressure ventilation or endotracheal intubation and mechanical ventilation or shock, defined as systolic blood pressure <90 mm hg or diastolic blood pressure <60 mm hg or requiring vasopressors or multi-organ dysfunction/failure (who clinical progression scale score ≥6) hospitalisation for reasons other than severity of covid-19 or comorbidities (e.g. social reasons, local policies, isolation/quarantine). active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer). history of significant haemorrhage (requiring hospitalisation or transfusion) outside of a surgical setting within the last 24 months. familial bleeding diathesis. glucose-6-phosphate dehydrogenase deficiency. severe hepatic and renal impairment as no safety and pk data of isoquercetin are available in these populations. current daily use of aspirin (> 81 mg daily), clopidogrel (plavix), cilostazol (pletal), aspirin-dipyridamole (aggrenox) (within 10 days) or considered to use regular use of higher doses of non-steroidal anti-inflammatory agents as determined by the treating physician (e.g. ibuprofen > 800 mg daily or equivalent). concomitant use of cyclosporine, warfarin (coumarin), tpa, strong inducer of cyp3a4, or substrate of cyp3a4 with narrow therapeutic index. history of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. pregnancy. because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. these potential risks may also apply to other agents used in this study. known hypersensitivity to isoquercetin, quercetin, or to any of the excipients used in the isoquercetin capsules. patient with history of poor compliance, or current or past psychiatric disease that might interfere with the ability to comply with the study procedures or give informed consent according to the judgment of the investigator or institutionalized by court decision. patient with any condition that the physician judges could be detrimental to patient participating in this study.

1. severe or critical covid-19, e.g.: - respiratory rate ≥ 30 breaths per minute or - heart rate ≥ 125 beats per minute or - respiratory failure, defined as clinical need for high-flow oxygen therapy, non- invasive positive pressure ventilation or endotracheal intubation and mechanical ventilation or - shock, defined as systolic blood pressure <90 mm hg or diastolic blood pressure <60 mm hg or requiring vasopressors or - multi-organ dysfunction/failure (who clinical progression scale score ≥6) 2. hospitalisation for reasons other than severity of covid-19 or comorbidities (e.g. social reasons, local policies, isolation/quarantine). 3. active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer). 4. history of significant haemorrhage (requiring hospitalisation or transfusion) outside of a surgical setting within the last 24 months. 5. familial bleeding diathesis. 6. glucose-6-phosphate dehydrogenase deficiency. 7. severe hepatic and renal impairment as no safety and pk data of isoquercetin are available in these populations. 8. current daily use of aspirin (> 81 mg daily), clopidogrel (plavix), cilostazol (pletal), aspirin-dipyridamole (aggrenox) (within 10 days) or considered to use regular use of higher doses of non-steroidal anti-inflammatory agents as determined by the treating physician (e.g. ibuprofen > 800 mg daily or equivalent). 9. concomitant use of cyclosporine, warfarin (coumarin), tpa, strong inducer of cyp3a4, or substrate of cyp3a4 with narrow therapeutic index. 10. history of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. 11. pregnancy. 12. because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. these potential risks may also apply to other agents used in this study. 13. known hypersensitivity to isoquercetin, quercetin, or to any of the excipients used in the isoquercetin capsules. 14. patient with history of poor compliance, or current or past psychiatric disease that might interfere with the ability to comply with the study procedures or give informed consent according to the judgment of the investigator or institutionalized by court decision. 15. patient with any condition that the physician judges could be detrimental to patient participating in this study.

1. severe or critical covid-19, e.g.: - respiratory rate ≥ 30 breaths per minute or - heart rate ≥ 125 beats per minute or - respiratory failure, defined as clinical need for high-flow oxygen therapy, non- invasive positive pressure ventilation or endotracheal intubation and mechanical ventilation or - shock, defined as systolic blood pressure <90 mm hg or diastolic blood pressure <60 mm hg or requiring vasopressors or - multi-organ dysfunction/failure (who clinical progression scale score ≥6) 2. hospitalisation for reasons other than severity of covid-19 or comorbidities (e.g. social reasons, local policies, isolation/quarantine). 3. active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer). 4. history of significant haemorrhage (requiring hospitalisation or transfusion) outside of a surgical setting within the last 24 months. 5. familial bleeding diathesis. 6. glucose-6-phosphate dehydrogenase deficiency. 7. severe hepatic and renal impairment as no safety and pk data of isoquercetin are available in these populations. 8. current daily use of aspirin (> 81 mg daily), clopidogrel (plavix), cilostazol (pletal), aspirin-dipyridamole (aggrenox) (within 10 days) or considered to use regular use of higher doses of non-steroidal anti-inflammatory agents as determined by the treating physician (e.g. ibuprofen > 800 mg daily or equivalent). 9. concomitant use of cyclosporine, warfarin (coumarin), tpa, strong inducer of cyp3a4, or substrate of cyp3a4 with narrow therapeutic index. 10. history of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. 11. pregnancy. 12. because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. these potential risks may also apply to other agents used in this study. 13. known hypersensitivity to isoquercetin, quercetin, or to any of the excipients used in the isoquercetin capsules. 14. patient with history of poor compliance, or current or past psychiatric disease that might interfere with the ability to comply with the study procedures or give informed consent according to the judgment of the investigator or institutionalized by court decision. 15. patient with any condition that the physician judges could be detrimental to patient participating in this study.