NEFL and COVID-19: The RE meta-analysis demonstrated that NfL levels in patients with moderate COVID-19 were significantly higher than in healthy controls (SMD = 0.80; 95% CI: 0.18, 1.42; p ≤ 0.01), with significant heterogeneity (I2: 89%; p ≤ 0.001) (third panel from the top, Figure 5).