When we performed protein-clinical trait correlation network analysis for COVID-19 severity, we found strong correlations (|r| > 0.5) between clinical features (CRP, SaO2/FiO2, and ventilation days) and specific nodal proteins (GM-CSF, CXCL10, TREM-1, CCL2/19, TF, IL-6/15, MPO, and S100A9) at the center of the network (Figure 6F). Here, S100A9 is linked to COVID-19.