The Receiver Operating Curve analysis indicated the rate of spike-specific IFNγ-releasing cells can discriminate correctly severe COVID-19 and mild-moderate patients (AUC: 0.9289; 95%CI: 0.8376–1.000; p< 0.0001), with a diagnostic specificity of 100% for s.f.c. > 81.2 x 106. The gene discussed is IFNG; the disease is COVID-19.