MMP9 and respiratory failure: Clinically, it has been reported that circulating MMP9 was distinct and early up-regulated in COVID-19 patients with respiratory failure.50 And Kawasaki-like disease has already been linked to coronavirus infections in children while Kawasaki disease is strongly related to a viral-induced epigenetic overexpression of MMP9.51 It is worth noting that MMP9 may play a key role in mediating viral invasion.