To quantify the magnitude of brain injury, we measured serum concentrations of blood brain-injury biomarkers using the Quanterix Simoa Neuro 4-PLEX B assay; concentrations of NfL, GFAP and total tau above the functional lower limit of quantification of the assays were detectable in most health control serum samples (NfL 99%, GFAP 69% and total tau 51%) and COVID-19 serum samples (NfL 97%, GFAP 73% and total tau 77%). Here, NEFL is linked to COVID-19.