An estimated 100 million people who have recovered from SARS-CoV-2 infection experience long-term sequelae (‘long COVID’), including ongoing cognitive impairment (‘brain fog’), but the mechanisms that cause this are poorly understood.

In this study, Greene et al. found that in people who experienced brain fog during acute SARS-CoV2 infection or long COVID, but not those who did not have brain fog, plasma levels of pro-inflammatory cytokines and S100β (a marker of blood–brain barrier (BBB) dysfunction) were increased.