Efficacy and Safety Study of BDB-001 in Severe COVID-19 With ALI/ARDS

Inclusion Criteria: 1. 18 years old ≤ age ≤ 80 years old, both men or women. 2. Confirmed SARS-CoV-2 infection, and meet at least one of the following criteria: Confirmed severe COVID-19 in no more than 5 days who meets any of the following criteria: 1. Respiratory distress, RR ≥ 30 times/min 2. Finger oxygen saturation (SpO2) ≤93% in resting state(room air) 3. Arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) ≤ 300 mmHg (1 mmHg = 0.133kpa) in supine position 4. Pulmonary imaging shows lesion progression \> 50% within 24-48 hours. Symptoms,signs or chest imaging indicates ALI/ARDS; 3. Requiring a mask oxygen therapy,high-flow nasal cannula oxygen therapy(HFNC). 4. The informed consent form signed. Exclusion Criteria: Subject who meets any of the following criteria will be excluded from the trial: 1. Subjects already progressed into critically severe COVID-19 Critical severe standards refer to FDA guidelines,as shown in Appendix 4 or sepsis and sepsis shock. 2. Concomitant with the following situation:severe lung disease such as chronic obstructive pulmonary disease (moderate to severe type), lung cancers, active tuberculosis; severe cardiovascular and cerebrovascular disease: unstable angina pectoris, myocardial infarction, postcardiac surgery, cardiac function ≥ grade 3 (NYHA Classification), or had undergone heart surgery within 6 months before randomization; severe liver diseases (e.g. Child-Pugh score ≥ grade C); severe kidney diseases, such as renal insufficiency (GFR ≤ 15 mL/min/1.73m\^2); immune deficiencies or immune-related diseases : including organ or bone marrow transplantation, some autoimmune diseases, IgG4-related diseases, allergic alveolitis, vasculitis; malignancies. 3. Subjects on current treatment with a complement inhibitor such as eculizumab within 1 month before randomization. 4. Subjects with hypersensitivity history to any ingredient contained in the drug. 5. A subject has used the following drugs within 2 weeks prior to screening procedures: * Calcineurin inhibitors (e.g., ciclosporin, tacrolimus, etc.) * Proliferation inhibitors (e.g., everolimus, sirolimus, etc.) * Anti-metabolic drugs (e.g., mycophenolate mofetil, mycophenolate, purine sulphate, etc.) * Recombinant human granulocyte macrophage colony stimulating factor (rhGM-CSF)/recombinant human granulocyte colony stimulating factor (rhG-CSF) 6. Pregnant or lactating woman. 7. Subjects who have participated in other interventional clinical trials in the last 3 months or during this trial. 8. Any other circumstances that the investigator considers inappropriate for the participation in this study.