This study is a multicenter, randomized, double-blind, placebo-controlled clinical trial to evaluate the safety and efficacy of Menstrual blood-derived Mesenchymal Stem Cells (SC01009) injection for the treatment of severe pneumonia caused by viruses. The purpose of the study is to assess the safety and efficacy of SC01009 injection in combination with standard treatment in patients with severe pneumonia caused by viruses. Viral pneumonia refers to acute inflammation of the lung parenchyma and/or interstitium caused by viral infections, which often leads to varying degrees of hypoxia and infection symptoms in the body, typically manifesting as fever, cough, wheezing, shortness of breath, and moist rales in the lungs, along with abnormalities in chest imaging \[such as X-rays, computed tomography (CT), etc.\]. Viral severe pneumonia is aggressive in onset, initially presenting with fever, cough, and rhinorrhea; it then rapidly progresses to severe toxic symptoms, with respiratory manifestations including cough and dyspnea, producing white mucoid sputum, purulent sputum, or pink frothy sputum. Severely ill patients are often in a critical state of life, endangering the patient's circulatory system and being in a state of respiratory failure requiring ventilator support. Active treatment of viral severe pneumonia, with appropriate measures, can lead to complete recovery of pulmonary function. If respiratory failure or poor circulatory function occurs and ultimately cannot be corrected, the prognosis is poor. Viral severe pneumonia follows clinical pathways (antiviral treatment guidelines and antiviral drug instructions) for antiviral treatment and appropriate adjunctive therapy. Mesenchymal stem cells (MSCs) are a type of multipotent stem cell with the potential for self-renewal and differentiation, characterized by self-renewal, multilineage differentiation, low immunogenicity, and paracrine functions, capable of homing to damaged areas, promoting epithelial tissue repair, suppressing inflammation, and inhibiting abnormal proliferation of fibroblasts. SC01009 injection is a cellular therapy product developed by Zhejiang Shengchuang Precision Medical Technology Co., Ltd., with its active ingredient being Menstrual blood-derived Mesenchymal Stem Cells (Men-MSCs). Men-MSCs are derived from allogeneic endometrial tissue of women, and preclinical studies have shown that SC01009 is safe and effective in animals, supporting further clinical development.