CD4 and COVID-19: Patients with severe COVID-19 and severe influenza A had a significantly lower number of total T cells (P = 0.001 and P < 0.0001, respectively), CD4+ T cells (P = 0.001 and P < 0.0001, respectively), and CD8+ T cells (P = 0.002 and P < 0.0001, respectively) than healthy controls in group two.