Many known signature-genes identified for COVID-19 (IFI27, OLFM4), RSV-LRTI (SIGLEC1, ISG15, IFI44) and PTB (MMP8, MMP9, DEFA1, DEFA1B, DEFA3 and DEFA4) are known to be associated with progressive severity87, showing the reproducibility of our findings. This evidence concerns the gene MMP9 and COVID-19.