IL2 and COVID-19: For IL-2 in COVID-19 patients, increased serum IL-2 levels were observed in nonsevere and severe patients than that in healthy controls (WMD = 0.46, 95% CI: 0.20-0.73, and P < 0.01; WMD = 0.70, 95% CI: 0.50-0.89, and P < 0.01) (Figures 3(a) and 3(b)), while no significant difference in IL-2 levels between severe and nonsevere patients (P = 0.54) (Figure 3(c)).