As shown in Figure 6, in the training data set GSE164805 of COVID‐19, all six hub genes (MMP9, ATF3, FCGR3B, CYBB, CCL4, and RELA) showed a significant diagnostic value with high AUC values (0.90, 1.00, 1.00, 1.00, 1.00 and 0.94, respectively). Here, MMP9 is linked to COVID-19.