DEFA4 and viral infectious disease: Finally, we compared the results of our single-gene OLAH classifier and our 3-gene classifier to a previously published 6-gene classifier (HK3, LY86, TGFB1, DEFA4, BATF, and HLA-DPB1) that was developed in non–COVID-19 viral infections and previously tested in patients with COVID-19 (28).