inclusion criteria: * male and female of ≥18years at time of enrollment; * subject (or legally authorized representative \[lar\]) is able and willing to provide written or verbal informed consent, which includes compliance with study requirements and restrictions listed in the consent form. * female subjects must agree to use an approved highly effective birth control (bc) method (\<1% failure rate per year) throughout the study (until completion of the day 85 follow-up visit), unless documented to have a reproductive status of non-childbearing potential or is postmenopausal: 1. non-childbearing potential defined as pre-menopausal female with medical history of bilateral tubal ligation, bilateral oophorectomy (removal of the ovaries), or hysterectomy; hysteroscopic sterilization, 2. postmenopausal defined as 12 months of spontaneous amenorrhea * woman of childbearing potential (wcbp) who is already using an established method of highly effective contraception or agrees to use one of the allowed bc methods listed in the protocol, for at least 28 days prior to the start of dosing (as determined by the investigator or designee) to sufficiently minimize the risk of pregnancy throughout study participation (until completion of the day 90 follow-up visit). * hospitalized participants with severe covid-19（6-8 point on who 10-point ordinal scale): 1. point 6: oxygen by niv or high flow; 2. point 7: intubation and mv, po2/fio2 ≥ 150 mmhg or spo2/fio2 ≥ 200 mmhg; 3. point 8: mv po2/fio2 \< 150 mmhg (or spo2/fio2 \< 200 mmhg) or vasopressors . * biological samples (not limited to any specific type) collected within 72 hours (allow retesting for potential subjects that tested positive beyond 72 hours) before randomization is laboratory-confirmed as sars-cov-2 infection (pcr, etc.); * ≤ 14 days since the onset of covid-19 symptoms.

inclusion criteria: * male and female of ≥18years at time of enrollment; * subject (or legally authorized representative \[lar\]) is able and willing to provide written or verbal informed consent, which includes compliance with study requirements and restrictions listed in the consent form. * female subjects must agree to use an approved highly effective birth control (bc) method (\<1% failure rate per year) throughout the study (until completion of the day 85 follow-up visit), unless documented to have a reproductive status of non-childbearing potential or is postmenopausal: 1. non-childbearing potential defined as pre-menopausal female with medical history of bilateral tubal ligation, bilateral oophorectomy (removal of the ovaries), or hysterectomy; hysteroscopic sterilization, 2. postmenopausal defined as 12 months of spontaneous amenorrhea * woman of childbearing potential (wcbp) who is already using an established method of highly effective contraception or agrees to use one of the allowed bc methods listed in the protocol, for at least 28 days prior to the start of dosing (as determined by the investigator or designee) to sufficiently minimize the risk of pregnancy throughout study participation (until completion of the day 90 follow-up visit). * hospitalized participants with severe covid-19（6-8 point on who 10-point ordinal scale): 1. point 6: oxygen by niv or high flow; 2. point 7: intubation and mv, po2/fio2 ≥ 150 mmhg or spo2/fio2 ≥ 200 mmhg; 3. point 8: mv po2/fio2 \< 150 mmhg (or spo2/fio2 \< 200 mmhg) or vasopressors . * biological samples (not limited to any specific type) collected within 72 hours (allow retesting for potential subjects that tested positive beyond 72 hours) before randomization is laboratory-confirmed as sars-cov-2 infection (pcr, etc.); * ≤ 14 days since the onset of covid-19 symptoms.

inclusion criteria: male and female of ≥18years at time of enrollment; subject (or legally authorized representative [lar]) is able and willing to provide written or verbal informed consent, which includes compliance with study requirements and restrictions listed in the consent form. female subjects must agree to use an approved highly effective birth control (bc) method (<1% failure rate per year) throughout the study (until completion of the day 85 follow-up visit), unless documented to have a reproductive status of non-childbearing potential or is postmenopausal: non-childbearing potential defined as pre-menopausal female with medical history of bilateral tubal ligation, bilateral oophorectomy (removal of the ovaries), or hysterectomy; hysteroscopic sterilization, postmenopausal defined as 12 months of spontaneous amenorrhea woman of childbearing potential (wcbp) who is already using an established method of highly effective contraception or agrees to use one of the allowed bc methods listed in the protocol, for at least 28 days prior to the start of dosing (as determined by the investigator or designee) to sufficiently minimize the risk of pregnancy throughout study participation (until completion of the day 90 follow-up visit). hospitalized participants with severe covid-19（6-8 point on who 10-point ordinal scale): point 6: oxygen by niv or high flow; point 7: intubation and mv, po2/fio2 ≥ 150 mmhg or spo2/fio2 ≥ 200 mmhg; point 8: mv po2/fio2 < 150 mmhg (or spo2/fio2 < 200 mmhg) or vasopressors . biological samples (not limited to any specific type) collected within 72 hours (allow retesting for potential subjects that tested positive beyond 72 hours) before randomization is laboratory-confirmed as sars-cov-2 infection (pcr, etc.); ≤ 14 days since the onset of covid-19 symptoms.

inclusion criteria: male and female of ≥18years at time of enrollment; subject (or legally authorized representative [lar]) is able and willing to provide written or verbal informed consent, which includes compliance with study requirements and restrictions listed in the consent form. female subjects must agree to use an approved highly effective birth control (bc) method (<1% failure rate per year) throughout the study (until completion of the day 85 follow-up visit), unless documented to have a reproductive status of non-childbearing potential or is postmenopausal: non-childbearing potential defined as pre-menopausal female with medical history of bilateral tubal ligation, bilateral oophorectomy (removal of the ovaries), or hysterectomy; hysteroscopic sterilization, postmenopausal defined as 12 months of spontaneous amenorrhea woman of childbearing potential (wcbp) who is already using an established method of highly effective contraception or agrees to use one of the allowed bc methods listed in the protocol, for at least 28 days prior to the start of dosing (as determined by the investigator or designee) to sufficiently minimize the risk of pregnancy throughout study participation (until completion of the day 90 follow-up visit). hospitalized participants with severe covid-19（6-8 point on who 10-point ordinal scale): point 6: oxygen by niv or high flow; point 7: intubation and mv, po2/fio2 ≥ 150 mmhg or spo2/fio2 ≥ 200 mmhg; point 8: mv po2/fio2 < 150 mmhg (or spo2/fio2 < 200 mmhg) or vasopressors . biological samples (not limited to any specific type) collected within 72 hours (allow retesting for potential subjects that tested positive beyond 72 hours) before randomization is laboratory-confirmed as sars-cov-2 infection (pcr, etc.); ≤ 14 days since the onset of covid-19 symptoms.

inclusion criteria: - male and female of ≥18years at time of enrollment; - subject (or legally authorized representative [lar]) is able and willing to provide written or verbal informed consent, which includes compliance with study requirements and restrictions listed in the consent form. - female subjects must agree to use an approved highly effective birth control (bc) method (<1% failure rate per year) throughout the study (until completion of the day 85 follow-up visit), unless documented to have a reproductive status of non-childbearing potential or is postmenopausal: 1. non-childbearing potential defined as pre-menopausal female with medical history of bilateral tubal ligation, bilateral oophorectomy (removal of the ovaries), or hysterectomy; hysteroscopic sterilization, 2. postmenopausal defined as 12 months of spontaneous amenorrhea - woman of childbearing potential (wcbp) who is already using an established method of highly effective contraception or agrees to use one of the allowed bc methods listed in the protocol, for at least 28 days prior to the start of dosing (as determined by the investigator or designee) to sufficiently minimize the risk of pregnancy throughout study participation (until completion of the day 90 follow-up visit). - hospitalized participants with severe covid-19（6-8 point on who 10-point ordinal scale): 1. point 6: oxygen by niv or high flow; 2. point 7: intubation and mv, po2/fio2 ≥ 150 mmhg or spo2/fio2 ≥ 200 mmhg; 3. point 8: mv po2/fio2 < 150 mmhg (or spo2/fio2 < 200 mmhg) or vasopressors . - biological samples (not limited to any specific type) collected within 72 hours (allow retesting for potential subjects that tested positive beyond 72 hours) before randomization is laboratory-confirmed as sars-cov-2 infection (pcr, etc.); - ≤ 14 days since the onset of covid-19 symptoms.

inclusion criteria: - male and female of ≥18years at time of enrollment; - subject (or legally authorized representative [lar]) is able and willing to provide written or verbal informed consent, which includes compliance with study requirements and restrictions listed in the consent form. - female subjects must agree to use an approved highly effective birth control (bc) method (<1% failure rate per year) throughout the study (until completion of the day 85 follow-up visit), unless documented to have a reproductive status of non-childbearing potential or is postmenopausal: 1. non-childbearing potential defined as pre-menopausal female with medical history of bilateral tubal ligation, bilateral oophorectomy (removal of the ovaries), or hysterectomy; hysteroscopic sterilization, 2. postmenopausal defined as 12 months of spontaneous amenorrhea - woman of childbearing potential (wcbp) who is already using an established method of highly effective contraception or agrees to use one of the allowed bc methods listed in the protocol, for at least 28 days prior to the start of dosing (as determined by the investigator or designee) to sufficiently minimize the risk of pregnancy throughout study participation (until completion of the day 90 follow-up visit). - hospitalized participants with severe covid-19（6-8 point on who 10-point ordinal scale): 1. point 6: oxygen by niv or high flow; 2. point 7: intubation and mv, po2/fio2 ≥ 150 mmhg or spo2/fio2 ≥ 200 mmhg; 3. point 8: mv po2/fio2 < 150 mmhg (or spo2/fio2 < 200 mmhg) or vasopressors . - biological samples (not limited to any specific type) collected within 72 hours (allow retesting for potential subjects that tested positive beyond 72 hours) before randomization is laboratory-confirmed as sars-cov-2 infection (pcr, etc.); - ≤ 14 days since the onset of covid-19 symptoms.