CD8A and COVID-19: In addition, the ratio of CD4+ and CD8+ T cells and the CD4+ T cell counts were found to be risk factors for all COVID-19 phenotypes (CD4+ T/8+ T: OR = 1.02–1.14, p = 7.21 × 10–9–4.63 × 10–3, Fig. 3C–E; CD4+ T: OR = 1.07–1.31, p = 3.17 × 10–4–3.42 × 10–3), while CD8+ T cell counts had a protective causal effect on critically ill (OR = 0.84, p = 3.83 × 10–3) and hospitalized COVID-19 cases (OR = 0.91, p = 2.17 × 10–2), respectively (Table 3) (Fig. 3F, G).