Existing studies have reported that viral infections induce the production of IL-12 to defend against infections.189–191 For instance, during influenza virus infection, IL-12 is endogenously produced to induce the secretion of IFN-γ from Th1 and NK cells, thereby inhibiting viral replication.190 A previous study reported elevated plasma levels of IL-12 in patients infected by SARS-CoV.192 However, Huang et al.9 recently found that the plasma levels of IL-12p70 showed no difference between COVID-19 patients and healthy adults. This evidence concerns the gene IFNG and COVID-19.