MMP9 and COVID-19: Recent evidence further expands the concept of dual role of MMP-9 in health and disease [6,7,8]: Elevated serum MMP-9 levels are strongly associated with severe outcomes in acute inflammatory syndromes such as COVID-19 (with the significant weighted mean difference ~246 ng/mL in severe versus non-severe cases), indicating that MMP-9 upregulation parallels systemic proteolytic burden and acute tissue injury [9].