F2 and infection: Although many specific hematologic indicators have been reported to be strongly associated with severe COVID-19 cases, with low levels of PLTs count, lymphocyte count and percentage, total protein, and high levels of D-dimer, leukocyte count, CRP, creatinine, neutrophil count and percentage, creatine kinase activity, and prolonged prothrombin time to be changed the most (30, 72, 73), the pathogenesis and detailed mechanisms of COVID-19, especially at early stage of infection is still largely unknown.