IL6 and influenza: A comparable relationship between subacute brain injury biomarkers and pro-inflammatory cytokine concentrations was seen in the influenza cohort (e.g. TNFa versus NfL and GFAP: ρ = 0.56, P = 0.0001 and ρ = 0.60, P < 0.0001, respectively, and IL-6 versus NfL and GFAP: ρ = 0.35, P = 0.02 and ρ = 0.36, P = 0.02, respectively).