Based on the presented results, we singled out IL-2/INFγ ratio as the strongest marker for a critical course of COVID-19 among hospitalized patients with SARS-CoV-2 infection, with the area under the ROC curve (AUC) being 0.859 (95%CI:0.780–0.939), and with 73.5% specificity and 90% sensitivity. Here, IL2 is linked to COVID-19.