Han et al. (19) enrolled 102 COVID-19 patients, classifying them into moderate, severe, and critical groups according to their symptoms with 45 control samples of healthy volunteers included, showing that COVID-19 patients have higher serum levels of cytokines (TNF-α, IFN-γ, IL-2, IL-4, IL-6, and IL-10) and CRP than control individuals, and within different severity COVID-19 groups, serum IL-6 and IL-10 levels are found to be predictive of disease severity. Here, IL4 is linked to COVID-19.