CD4 and infection: We reviewed the patients’ data of 94 healthy blood donors, 80 Non-severe-COVID-19, 19 Severe-COVID-19 and 37 severe influenza A. We found total lymphocytes (0.81 × 109/L vs 1.74 × 109/L, P = 0.001; 0.87 × 109/L vs 1.74 × 109/L, P < 0.0001, respectively) and lymphocyte subsets (T cells, CD4+ and CD8+ T cell subsets) of severe COVID-19 and severe influenza A patients to be significantly lower than those of healthy donors at early infection stages.