MB and COVID-19: The association between old age and severe or critical type COVID‐19 might be due to reduced immune function, as reflected by increased neutrophil and decreased lymphoncyte percentages, and poor nutrition, reflected by decreased Hb, albumin; inflammatory factor storm, reflected by increased ESR, CRP, and PCT; impaired coagulation function, liver, kidney, heart function, reflected by increased DD, ALT, BUN, Mb and decreased Pt.