CD4 and COVID-19: In COVID-19 patients, total lymphocytes, CD4+ T cells, CD8+ T cells, B cells, and NK cells were found to be decreased (Wang et al., 2020a; Anka et al., 2021), and for data from blood tests at admission, lymphocyte counts were found to be significantly lower in patients with severe disease than in patients with mild disease (0.9×109 cells/L [range 0.8–0.9] versus 1.2 [1.0–1.6]; p = 0.011) (Zhou et al., 2020).