IL4 and COVID-19: Serum IL-4 levels were elevated in nonsevere COVID-19 patients compared to healthy individuals (WMD = 0.43, 95% CI: 0.20-0.65, and P < 0.01) (Figure 4(a)), while no significant difference in IL-4 levels was observed between healthy controls and severe patients, as well as between severe and nonsevere COVID-19 patients (P > 0.05) (Figures 4(b) and 4(c)).