NEFL and COVID-19: In COVID-19 patients, a correlation was found between the levels of neuroaxonal damage biomarkers, NfL and T-tau (r = 0.583; p < 0.001), but also between NfL and GFAP (r = 0.671; p < 0.001) and between T-tau and GFAP (r = 0.667; p < 0.001) (Figure 2).