Data extraction and analysis
All studies that met the above-mentioned criteria were carefully analyzed and strictly reviewed. We collected relevant clinical information including the population data (e.g. age, gender), number of patients in the studies, and documented clinical manifestations. Full-text versions of relevant articles were reviewed, and clinical characteristics were extracted. The Newcastle-Ottawa quality assessment scale (NOS) was used to evaluate the quality of included studies12. A scale ranges from 0 to 9, with higher points indicating higher quality was applied. The two authors (WJ and XG) used a unified data table to extract data independently, and resolved controversial issues through further discussion. We define severe COVID-19 pneumonia as the disease status that requires intensive care unit (ICU) admission with respiratory/circulatory support10,11,13,14, which is in align with the guideline from the World Health Organization (WHO). We compared the clinical characteristics of severe and non-severe COVID-19 pneumonia, followed by a meta-analysis using three high quality China-based studies.