CD4 and COVID-19: Studies have found that the absolute number of T-lymphocytes, CD4+ T-cells, and CD8+ T-cells in COVID-19 patients with severe-critical condition is lower than in patients with mild-moderate condition, hypothesized as an impact of direct SARS-CoV-2 infection to T-lymphocytes, specifically CD4+ and CD8+ T-cells (Shen et al., 2022; Wen et al., 2021).