To quantify NET fragments, we performed immunofluorescence staining on paraffin-embedded lung sections from SARS-CoV-2-infected mice or from COVID-19 patients with anti-MPO and anti-H3Cit antibodies together with 4′,6-diamidino-2-phenylindole (DAPI), and we defined DAPI+ MPO+ H3Cit + as a NET-positive area. This evidence concerns the gene MPO and COVID-19.