The present study is the largest study to date to assess complement activation markers C5a, C5b-9 as well as endothelial cell activation markers E-selectin, ICAM-1 and VCAM-1 and Galectin-3, an immunoregulatory protein, in COVID-19 cases and SARS-CoV-2 negative controls with similar symptoms and presentation. Here, C5 is linked to COVID-19.