MMP9 and COVID-19: Besides MMP-9, which has been shown to be associated with a high risk of mortality, others, such as MMP-1 [11,68,87,98,100], MMP-2 [67], MMP-8 [91], and MMP-13 [58,136] have also been correlated with disease severity and increased risk of death, especially during the acute phase of COVID-19.