Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [I

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [I

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having a

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having a

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 9

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 9

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. M

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-r

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-r

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. Male subjects must have documented vasectomy or if sexually active must agree to use a highly effective method of contraception

Subjects who meet any of the following exclusion criteria will not be eligible for study enrollment. General Exclusion Criteria 1. Onset of COVID-19 symptoms > 14 days from randomization 2. Hospitalized > 7 days prior to randomization 3. [For Cohort 1 only] Need for invasive mechanical ventilation 4. Need for ECMO 5. Serious prior or concomitant illness that in the opinion of the Investigator precludes the subject from enrolling in the trial, including (but not limited to): • History of pulmonary alveolar proteinosis (PAP) • History of immunodeficiency (congenital or acquired) • History of solid-organ or bone marrow transplant • Current systemic autoimmune or autoinflammatory disease(s) requiring systemic immune-modulating drugs • History of or active cancer within the last 10 years - except for basal and squamous cell carcinoma of the skin or in situ carcinoma of the cervix treated and considered cured • Severe and uncontrolled pulmonary disease other than COVID-19 pneumonia (eg, asthma, chronic obstructive pulmonary disease [COPD], or others) • Pre-existing severe left ventricular systolic dysfunction (ie, left ventricular ejection fraction [LVEF] < 35%) • Known active tuberculosis (TB) determined by history and local standard of care, or history of incompletely treated TB or at high risk for latent TB (exposure or prior incarceration) • Concomitant uncontrolled systemic bacterial or fungal infection • Concomitant respiratory viral infection other than COVID-19 that, in the opinion of the Investigator, represents a higher mortality risk (eg, SARS, MERS) • History of chronic liver disease with portal hypertension 6. Recent treatment with cell-depleting biological therapies (eg, anti-CD20) within 12 months, cell-depleting biological therapies (such as anti-TNF, anakinra, anti-IL-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine A, azathioprine, cyclophosphamide, mycophenolate mofetil (MMF), COVID-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization 7. Recent treatment with intramuscular live (attenuated) vaccine within 4 weeks prior to randomization 8. Corrected QT interval by Federicia method (QTcF) on Screening ECG &#8805,450ms 9. Chronic or recent (within 1 month) corticosteroid use > 10 mg/day 10. Enrolled in another investigational study of a medical intervention within 30 days prior to randomization 11. Known hypersensitivity to mavrilimumab or any of its excipients 12. In the opinion of the Investigator, unable to comply with the requirements to participate in the study 13. Female subjects must be: • postmenopausal, defined as at least 12 months post cessation of menses (without an alternative medical cause), or • permanently sterile following documented hysterectomy, bilateral salpingectomy, bilateral oophorectomy, or tubal ligation or having a male partner with vasectomy as affirmed by the subject, or • nonpregnant, nonlactating, and if sexually active having agreed to use a highly effective method of contraception (ie, hormonal contraceptives associated with inhibition of ovulation or intrauterine device [IUD], or intrauterine hormone-releasing system [IUS], or sexual abstinence) from Screening Visit until Day 90. 14. Male subjects must have documented vasectomy or if sexually active must agree to use a highly effective method of contraception