CD4 and COVID-19: Patients with severe COVID-19 are more likely to exhibit lymphopenia on admission, indicating a significant predictor for severe patients.9,10 Patients also show a marked reduction in CD4+ T, CD8+ T, NK, and B cell number.2,11–13 Lymphocyte percentages were found to be lower than 20% in severe cases.14 Further analysis showed a significant decrease in T cell counts, especially CD8+ T cells in severe cases compared with mild cases.15 Qin et al.12 reported that the percentage of memory helper T cells (CD3+CD4+CD45RO+) is also decreased in severe cases compared with non-severe cases.