GFAP and COVID-19: Among the excluded studies, 15 did not report outcomes of interest (NfL and GFAP) in both COVID-19 and healthy controls [30,31,38,39,40,41,42,43,44,45,46,47,48,49,50], six did not include healthy controls [31,36,38,44,48,51], three were reviews [8,52,53], and two were editorial reports [54,55]; note that a few reports belonged to more than one category.