Safety and Efficacy of Umbilical Cord Mesenchymal Stem Cell Exosomes in Treating Chronic Cough After COVID-19

Inclusion Criteria: * Trial participants voluntarily participate in this study and sign an informed consent form. * At the time of signing the informed consent form, the age of the subject should be ≥18 or ≤80 years old, with no gender restrictions. * The subject has been diagnosed with COVID-19 (confirmed by positive nucleic acid or antigen test) and has symptoms that have lasted for more than 4 weeks. * Negative nucleic acid or antigen test at the time of screening. * The subject has had continuous or intermittent coughing, or loss of taste/smell for ≥4 weeks, which did not occur before the onset of COVID-19 infection. * No prior treatment with umbilical cord mesenchymal stem cell-derived extracellular vesicles. * The patient fully understands the purpose and requirements of this clinical study and is willing to complete all trial procedures according to the study requirements. Exclusion Criteria: * Age ≤18 or ≥80 years old. * Acute COVID-19 patients. * Suspected or confirmed to have severe, active bacterial, fungal, or other infections that may pose a risk when intervention measures are taken, as determined by the researcher. * Patients with a history of diagnosed bronchial asthma, cough variant asthma, or chronic cough; patients with other pulmonary diseases such as chronic obstructive pulmonary disease, bronchiectasis, tuberculosis, lung cancer, etc. * Any of the following during the screening period: 1) ALT or AST \> 3 times the upper limit of normal; 2) eGFR \<60 mL…