NEFL and COVID-19: Given the multiple comparisons above, we performed a sensitivity analysis using a mixed effects model which confirmed that both severity and time point significantly affected both GFAP (P = 0.0017 and P < 0.0001) and NfL (P = 0.003 and P < 0.0001), but not total tau (P = 0.81 and P = 0.71) concentrations in the serum of COVID-19 patients.