This is a multicenter, double-blind, randomized, placebo-controlled phase 2/3 clinical study. Based on the results of the Phase I clinical study, one repeat dose group and one placebo group are used for the standard treatment of the Novel Coronavirus Pneumonia Protocol (Trial 8) The treatment regimen is a one-time intravenous infusion of either mprozumab or placebo on day 1 (D1) and day 8 (D8) of the treatment period at a dose of 0.2 mg/kg based on body weight. An estimated 150 subjects will be randomly assigned to either Meplazumab or placebo in a 2:1 ratio A short-term efficacy evaluation was performed to determine the efficacy and safety of Meplazumab in each subject within 14 days of initial administration and a long-term follow-up evaluation was performed 28 days after initial administration to determine the safety of Meplazumab.

Inclusion Criteria:

• 18 years ≤Subject ≤ 75 years, Male and/or female;
• Clinical confirmation of COVID-19 patients in accordance with novel Coronavirus Diagnosis and Treatment Protocol (Trial Version 8) of the NHC
• Participants must be able to understand and willing to participate in this research, this study and signed informed consent form (if incapacitated subjects, the researchers believe the subjects to the test in its own interests, should be signed by its legal guardian informed consent, or telephone inform consent (recording) and note it in the original medical records and other relevant documents)

Exclusion Criteria:

• Subjects with any unstable conditions, a history of significant hypersensitivity, or known allergy to components of the investigational agent;
• SARS-CoV-2 infection by PCR ≥ 96h;
• Platelet (PLT) < 50×10^9/L, or hemoglobin (HGB) < 60g/L;
• Total bilirubin (TBIL) > 2×ULN (upper limit of normal value), or alanine transferase (ALT), aspartate transferase (AST), alkaline phosphatase (ALP) > 5×ULN;
• glomerular filtration rate (GFR) < 30mL/min·1.73m^2, or serum creatinine increased by 0.5mg/ dL within 7 days, or oliguria (<400mL/24hr), or anuria (<100mL/24hr);
• Pregnant or breast feeding;
• Persons who have family planning or do not agree to use effective non-drug contraceptive measures within 6 months after signing the ICF;
• Subjects participating in another clinical study. There will be a need for washout with 5 half lives depending on the study treatment or 30 days since any previous study, whichever is longer;
• he inestigators concluded that the patients had other reasons for not being eligible for the study.