Traditional Chinese Medicine or Low-dose Dexamethasone in COVID-19 Pneumonia

The goal of this type of clinical trial is to learn about symptomatic patients with post-COVID-19 parenchymal lung abnormalities. The main questions it aims to answer are: the efficacy and safety of low-dose dexamethasone or traditional Chinese medicine in symptomatic patients with post-COVID-19 parenchymal lung abnormalities. Participants will be divided into three parallel groups：controlled group with conventional western medicine treatment including oxygen therapy, antibiotics, nebulization therapy, etc. dexamethasone group: dexamethasone 1.5mg/day for one week and 0.75mg/day for another week basing on conventional western medicine. Chinese medicine group: Strengthening spleen and tonifying lung decoction for 2 weeks basing on conventional western medicine.