Among the immune factors found only in critical ill COVID-19, but not influenza, patients are interferon-gamma (IFN-γ), IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, IL-1β, C-C motif chemokine ligand 11 (CCL11), vascular endothelial growth factor (VEGF), tumor necrosis factor-like weak inducer of apoptosis (TWEAK), thymic stromal lymphopoietin (TSLP), MMP-1, and MMP-3 (Choreño-Parra and others 2021). Here, MMP3 is linked to COVID-19.