Inclusion Criteria: 

• Adults 18 years of age and older who are capable of providing informed consent or have a proxy capable of giving consent for them. See Section 10.1 for details on the consenting process for subjects with COVID-19.
• Virologic confirmation of SARS-CoV-2 infection via any diagnostic test for SARS-CoV- 2 authorized by US FDA or other national regulatory agency or ministry of health (e.g., qualitative SARS-CoV-2 real time polymerase chain reaction (RT-PCR), nucleic acid amplification (molecular) test, etc.) assessed locally per institution standard of care, prior to randomization.
• Pneumonia diagnosed by chest x-ray or computed tomography (CT) revealing infiltrates consistent with pneumonia. Note that a CT scan may be used if available, but is not required.
• Subject must have an SpO2 ≤ 94% on room air and/or require supplemental oxygen (including high-flow oxygen support or NPPV) to be eligible.
• Subject is hospitalized and has not required invasive mechanical ventilation during this hospitalization.
• Subject has not participated in other clinical trials for COVID-19 using an immunomodulating monoclonal antibody or kinase inhibitor. Subjects on corticosteroids, convalescent plasma, remdesivir or other anti-virals and/or hydroxychloroquine with or without azithromycin are not excluded from the study. Agents that have received emergency use authorization or approval from the FDA or are considered by the study site to be standard of care treatment at the institution for COVID-19 are permitted provided the agent is not an immunomodulating monoclonal antibody or kinase inhibitor. Participation in clinical trials with remdesivir or convalescent plasma is permitted provided the subject meets all other eligibility criteria.
• Females of childbearing potential must have a negative urine or serum pregnancy test at screening/baseline. Women of childbearing potential must agree to use adequate contraception (hormonal or barrier method of birth control, abstinence) prior to study entry and for 5 months following their last dose of study drug. A negative urine pregnancy test or serum beta human chorionic gonadotropin (β-hCG) is required for all women of childbearing potential within 1 week prior to receiving first dose of study drug.

Exclusion Criteria:

• Subject requires invasive mechanical ventilation or extracorporeal membrane oxygenation (i.e., category 2 on the ordinal scale).
• Confirmed diagnosis of bacterial pneumonia or other active/uncontrolled fungal or viral infections at screening/baseline.
• Known active tuberculosis (TB), history of incompletely treated TB or suspected or known extrapulmonary TB.
• Currently receiving treatment for hepatitis A, hepatitis B, hepatitis C or HIV infection.
• History of pulmonary alveolar proteinosis (PAP).
• Women of childbearing potential who are pregnant or breastfeeding.
• Known hypersensitivity to lenzilumab or any of its components.
• Use of any FDA approved anti-IL-6 (e.g., tocilizumab, sarilumab, sitlukimab), anti-IL-1 (e.g., anakinra, canakinumab) or kinase inhibitor (e.g., baracitinib, ibrutinib, acalabrutinib) therapy to treat COVID-19 within 8 weeks prior to randomization. Use of any neutralizing monoclonal antibodies such as bamlanivimab (LY-CoV555) or REGNCOV2 within 8 weeks prior to randomization. Subjects receiving other FDA-approved immunomodulators to treat underlying autoimmune disorders such as rheumatoid arthritis, psoriasis, ankylosing spondylitis, asthma, COPD, atopic dermatitis, multiple sclerosis, etc., would not be excluded unless there is a potential drug interaction with lenzilumab. Note: Subjects receiving convalescent plasma or corticosteroids are not excluded from the study. Note: Subjects receiving remdesivir or other anti-virals and/or hydroxychloroquine with or without azithromycin are not excluded from the study.
• Use of GM-CSF agents (e.g., sargramostim) within 2 months prior to randomization.
• Expected survival < 48h in the opinion of the investigator or subjects with Do Not Resuscitate or Do Not Intubate orders at baseline.
• Any condition that, in the opinion of the investigator, is likely to interfere with the safety and efficacy of the study treatment or puts the subject at unacceptably high risk from the study.