We observed significantly lower levels of MMP-9 at day 1 in pediatric COVID-19 patients compared to controls (28.14 (16.4,38.6) vs. 100.3 (67.2,882.6) μg/ml, p = 0.005) and UCHL-1 [2.2 (0.7,16.3) vs. 35.2 (10.7,54.3) ng/ml, p = 0.013). Here, MMP9 is linked to COVID-19.