Efficacy and Safety of Umbilical Cord Mesenchymal Stem Cells in the Treatment of Long COVID-19

Inclusion Criteria: 1. The age ranges from 18 to 85 (inclusive), regardless of gender. 2. Patients with Confirmed SARS-CoV-2 infection, according to the consensus of the Chinese diagnostic criteria for COVID-19 (Tentative tenth Edition). 3. Patients with symptoms of long COVID-19 3 months from the onset of COVID-19, lasting for at least 2 months, and the symptoms cannot be explained by other diseases. 4. Be expected to live longer than 1 year. 5. Volunteer to participate in this clinical study and sign the written informed consent. Exclusion Criteria: 1. Those who are using immunosuppressive drugs or long-term immunosuppressive drugs after organ transplantation. 2. T lymphocyte abnormality, HIV positive. 3. Highly allergic or have a history of severe allergy. 4. Pregnant and lactating women. 5. Patients with severe autoimmune disease history; 6. Patients with uncontrolled chronic diseases or serious complications; 7. Patients with malignant tumors; 8. Patients with pulmonary embolism, acute coronary syndrome, cerebral embolism or at high risk of thromboembolism; 9. Patients with severe organ dysfunction 10. Other situations that the researchers think are not suitable for participating in this study