The biomarkers of oxidative stress confirmed that the infection possesses a free radical damage mechanism: TBARSs were increased almost 3-fold, AOC was reduced more than 4-fold, SOD was increased almost 5-fold, CAT was increased 1.4-fold, and GRA was suppressed 2.5-fold in the patients with “pure” COVID-19 infection. This evidence concerns the gene CAT and infection.