F2 and influenza: In comparison with the COVID-19 cohort, the influenza cohort possessed substantially reduced prothrombin time and aPTT, but increased thrombin time and fibrinogen level, and greatly elevated D-dimer concentration; in comparison with the COVID-19 Δ cohort, the influenza cohort owned similar prothrombin time and reduced aPTT and thrombin time, but augmented fibrinogen and D-dimer levels.