CD8A and COVID-19: This observation is similar to our previous finding in influenza virus H7N9, wherein early robust virus-specific CD8+ T cells contributed to the control of disease progression.18 A suboptimal virus-specific CD8+ T cell response characterized by a weaker magnitude and slightly delayed peaking at 17 dps (Fig. 2d, e), manifested in severe COVID-19 cases (Supplementary Table 2).