NEFL and viral infectious disease: Regarding critically ill COVID-19 patients, it is still unknown whether there is direct damage to the CNS from the virus infection or whether it is multifactorial genesis due to hypoxia, coagulopathy etc. In a study of 47 patients with moderate (hospitalized requiring supplemental oxygen) and critical (admitted to the ICU) COVID-19, NfL and GFAp were elevated at onset of symptoms and after 11 days, with an early peak of GFAp and sustained elevated levels of NfL, showing evidence of neuronal injury and glial activation18.