Even Mild Covid-19 May Cause Lasting Brain Fog

In previous installments of this series, we looked at new research that suggests even mild SARS-CoV-2 infection can impair cognitive function. The first step in this chain of events happens when the virus sets off an intense inflammatory response that eventually reaches the brain. Once there, inflammation triggers reactivity of microglial cells —the resident immune cells of the central nervous system— which produce yet more inflammation and interfere with the normal functioning of important cells, including oligodendrocytes and neural precursor cells (Figure 1). Schematic of the pathway through which general inflammation causes cognitive dysfunction. But given that all of this happens off the back of inflammation, which we experience during any number of infections or injuries, wouldn’t we expect to see something similar unfold in other viral diseases? As part of their research, Fernández-Castañeda et al. asked themselves this same question. In the search for an answer, they turned to influenza. Like Covid-19, the flu has also been associated with cognitive and neurological issues. And like SARS-CoV-2, influenza is rarely neuroinvasive — even though both viruses can infect the brain directly, as can many other viruses, it seems to happen only infrequently. It could be, then, that influenza causes cognitive issues through a similar mechanism as Covid.