stage i: * not expected to survive for more than 24 hours * underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (eg, motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) * severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing * congestive heart failure, defined as new york heart association class iv * acute left ventricular failure or myocardial infarction * currently receiving extracorporeal membrane oxygenation (ecmo) therapy * receiving renal dialysis therapy for chronic renal failure * moderate to severe liver failure (childs-pugh score \>12) * presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years * lung transplant patient * who class iii or iv pulmonary hypertension * documented deep venous thrombosis or pulmonary embolism within past 3 months * major trauma in the preceding 5 days * concurrent treatment with immune modulatory study drugs (e.g., anti-il6 antibodies, janus kinase (jak) kinase inhibitors) or other agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, prior to dosing with op-101; except for those that have received fda emergency-use authorization and have become standard of care (soc). concurrent treatment with corticosteroids is permitted if participant has documented continued hypoxemia (spo2 of \<95% on room air) and hyper-inflammation (crp\>=10 mg/l) at screening. * has lost or donated \>450 ml of whole blood or blood products within 30 days before screening * has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements * is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee. stage ii: * not expected to survive for more than 24 hours * underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (e.g., motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) * severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing * congestive heart failure, defined as new york heart association class iv * acute left ventricular failure or myocardial infarction * currently receiving ecmo therapy * receiving renal dialysis therapy for end stage renal disease * moderate to severe liver failure (childs-pugh score \>12) * presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years * lung transplant patient * who class iii or iv pulmonary hypertension * documented deep venous thrombosis or pulmonary embolism within past 3 months * major trauma in the preceding 5 days * concurrent treatment with approved or emergency use authorized immune modulatory study drugs (eg, anti-il6 antibodies \[tocilizumab\], jak kinase inhibitors \[baricitinib\]) or other investigational agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, before dosing with op-101. * has lost or donated \>450 ml of whole blood or blood products within 30 days before screening * mechanical ventilation for \>72 hours at the time of dosing * has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements * is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee.

stage i: * not expected to survive for more than 24 hours * underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (eg, motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) * severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing * congestive heart failure, defined as new york heart association class iv * acute left ventricular failure or myocardial infarction * currently receiving extracorporeal membrane oxygenation (ecmo) therapy * receiving renal dialysis therapy for chronic renal failure * moderate to severe liver failure (childs-pugh score \>12) * presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years * lung transplant patient * who class iii or iv pulmonary hypertension * documented deep venous thrombosis or pulmonary embolism within past 3 months * major trauma in the preceding 5 days * concurrent treatment with immune modulatory study drugs (e.g., anti-il6 antibodies, janus kinase (jak) kinase inhibitors) or other agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, prior to dosing with op-101; except for those that have received fda emergency-use authorization and have become standard of care (soc). concurrent treatment with corticosteroids is permitted if participant has documented continued hypoxemia (spo2 of \<95% on room air) and hyper-inflammation (crp\>=10 mg/l) at screening. * has lost or donated \>450 ml of whole blood or blood products within 30 days before screening * has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements * is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee. stage ii: * not expected to survive for more than 24 hours * underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (e.g., motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) * severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing * congestive heart failure, defined as new york heart association class iv * acute left ventricular failure or myocardial infarction * currently receiving ecmo therapy * receiving renal dialysis therapy for end stage renal disease * moderate to severe liver failure (childs-pugh score \>12) * presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years * lung transplant patient * who class iii or iv pulmonary hypertension * documented deep venous thrombosis or pulmonary embolism within past 3 months * major trauma in the preceding 5 days * concurrent treatment with approved or emergency use authorized immune modulatory study drugs (eg, anti-il6 antibodies \[tocilizumab\], jak kinase inhibitors \[baricitinib\]) or other investigational agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, before dosing with op-101. * has lost or donated \>450 ml of whole blood or blood products within 30 days before screening * mechanical ventilation for \>72 hours at the time of dosing * has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements * is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee.

stage i: not expected to survive for more than 24 hours underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (eg, motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing congestive heart failure, defined as new york heart association class iv acute left ventricular failure or myocardial infarction currently receiving extracorporeal membrane oxygenation (ecmo) therapy receiving renal dialysis therapy for chronic renal failure moderate to severe liver failure (childs-pugh score >12) presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years lung transplant patient who class iii or iv pulmonary hypertension documented deep venous thrombosis or pulmonary embolism within past 3 months major trauma in the preceding 5 days concurrent treatment with immune modulatory study drugs (e.g., anti-il6 antibodies, janus kinase (jak) kinase inhibitors) or other agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, prior to dosing with op-101; except for those that have received fda emergency-use authorization and have become standard of care (soc). concurrent treatment with corticosteroids is permitted if participant has documented continued hypoxemia (spo2 of <95% on room air) and hyper-inflammation (crp>=10 mg/l) at screening. has lost or donated >450 ml of whole blood or blood products within 30 days before screening has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee. stage ii: not expected to survive for more than 24 hours underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (e.g., motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing congestive heart failure, defined as new york heart association class iv acute left ventricular failure or myocardial infarction currently receiving ecmo therapy receiving renal dialysis therapy for end stage renal disease moderate to severe liver failure (childs-pugh score >12) presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years lung transplant patient who class iii or iv pulmonary hypertension documented deep venous thrombosis or pulmonary embolism within past 3 months major trauma in the preceding 5 days concurrent treatment with approved or emergency use authorized immune modulatory study drugs (eg, anti-il6 antibodies [tocilizumab], jak kinase inhibitors [baricitinib]) or other investigational agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, before dosing with op-101. has lost or donated >450 ml of whole blood or blood products within 30 days before screening mechanical ventilation for >72 hours at the time of dosing has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee.

stage i: not expected to survive for more than 24 hours underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (eg, motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing congestive heart failure, defined as new york heart association class iv acute left ventricular failure or myocardial infarction currently receiving extracorporeal membrane oxygenation (ecmo) therapy receiving renal dialysis therapy for chronic renal failure moderate to severe liver failure (childs-pugh score >12) presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years lung transplant patient who class iii or iv pulmonary hypertension documented deep venous thrombosis or pulmonary embolism within past 3 months major trauma in the preceding 5 days concurrent treatment with immune modulatory study drugs (e.g., anti-il6 antibodies, janus kinase (jak) kinase inhibitors) or other agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, prior to dosing with op-101; except for those that have received fda emergency-use authorization and have become standard of care (soc). concurrent treatment with corticosteroids is permitted if participant has documented continued hypoxemia (spo2 of <95% on room air) and hyper-inflammation (crp>=10 mg/l) at screening. has lost or donated >450 ml of whole blood or blood products within 30 days before screening has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee. stage ii: not expected to survive for more than 24 hours underlying clinical condition where, in the opinion of the investigator, it would be extremely unlikely that the patient would come off ventilation (e.g., motor neuron disease, duchenne muscular dystrophy, or rapidly progressive interstitial pulmonary fibrosis) severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing congestive heart failure, defined as new york heart association class iv acute left ventricular failure or myocardial infarction currently receiving ecmo therapy receiving renal dialysis therapy for end stage renal disease moderate to severe liver failure (childs-pugh score >12) presence of any active malignancy (other than nonmelanoma skin cancer) that required treatment within the last 2 years lung transplant patient who class iii or iv pulmonary hypertension documented deep venous thrombosis or pulmonary embolism within past 3 months major trauma in the preceding 5 days concurrent treatment with approved or emergency use authorized immune modulatory study drugs (eg, anti-il6 antibodies [tocilizumab], jak kinase inhibitors [baricitinib]) or other investigational agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, before dosing with op-101. has lost or donated >450 ml of whole blood or blood products within 30 days before screening mechanical ventilation for >72 hours at the time of dosing has any finding that, in the view of the investigator or medical monitor, would compromise the patient's safety requirements is employed by the sponsor, the contract research organization, or the study site (permanent, temporary contract worker, or designee responsible for the conduct of the study), or is a family member (spouse, parent, sibling, or child) of the sponsor, contract research organization, or study site employee.

- not expected to survive for more than 24 hours - severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing - acute left ventricular failure or myocardial infarction - currently receiving extracorporeal membrane oxygenation (ecmo) therapy - receiving renal dialysis therapy for chronic renal failure - concurrent treatment with immune modulatory study drugs (e.g., anti-il6 antibodies, janus kinase (jak) kinase inhibitors) or other agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, prior to dosing with op-101; except for those that have received fda emergency-use authorization and have become standard of care (soc). concurrent treatment with corticosteroids is permitted if participant has documented continued hypoxemia (spo2 of <95% on room air) and hyper-inflammation (crp>=10mg/l) at screening.

- not expected to survive for more than 24 hours - severe chronic obstructive pulmonary disease requiring long-term home oxygen therapy or mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure used solely for sleep-disordered breathing - acute left ventricular failure or myocardial infarction - currently receiving extracorporeal membrane oxygenation (ecmo) therapy - receiving renal dialysis therapy for chronic renal failure - concurrent treatment with immune modulatory study drugs (e.g., anti-il6 antibodies, janus kinase (jak) kinase inhibitors) or other agents with actual or possible direct acting antiviral activity against sars-cov-2 within 30 days or 5 half-lives, whichever is longer, prior to dosing with op-101; except for those that have received fda emergency-use authorization and have become standard of care (soc). concurrent treatment with corticosteroids is permitted if participant has documented continued hypoxemia (spo2 of <95% on room air) and hyper-inflammation (crp>=10mg/l) at screening.