Selection criteria

Studies were included if they met the following criteria: i) they contained clinical characteristics of SARS-CoV-2-confirmed patients and ii) they contained clinical characteristics of 2009 pandemic H1N1 influenza-confirmed patients. Studies were excluded if they met following criteria: i) they belonged to systematic review, meta-analysis, case reports, perspectives, or conference abstracts; ii) they were animal coronavirus studies; iii) they had no primary data or incomplete data; iv) they had duplicate data; and v) they were of low quality. Detailed full-text review and data extraction were independently performed by two investigators: PL and YW. The investigators resolved discrepancies by jointly reviewing the study in question. If no consensus was reached, another reviewer (QP) functioned as an arbiter to resolve disagreements.