Covid and the Brain

Eric Topol (Scripps Research Translational Institute) provides an interesting commentary on, what is currently the largest study, looking at the effects of Sars-CoV-2 infections on the brain (https://www.theguardian.com/commentisfree/2022/mar/09/covid-coronavirus-brain-study-eric-topol). There was actually some serendipity in how that data was generated. The subjects were individuals participating in the UK Biobank study. Their cohort had all had MRI brain scans and been subjected to basic cognitive tests, before the onset of the Covid19 pandemic. Three years later (after the early pandemic), some were brought back for retesting. About 400 had not had a Covid19 infection whereas about 400 had. In the latter group, most had had a mild to moderate infection, not requiring hospitalisation. The small number that did require hospitalisation, were removed from the study. The cohorts were not fully representative of the population. 97% were of white ethnicity. They also ranged in age from 47 to 80 years. The control group (the uninfected folk) showed a typical annual reduction in grey matter of 0.2%. The experimental group (those folk who had had a mild to moderate infection) had greater grey matter losses. In some cases, this was ten times that seen in controls. The neural losses were chiefly seen in the olfactory (sense of smell) region of the brain. A loss of the sense of smell was one of the symptoms of the earlier Covid19 infections. Omicron now seems to have a lesser impact on smell and taste but the subjects were unlikely to have been infected with this variant. The experimental group also showed reductions in cognitive test performances. There appeared, however, to be little differences between the groups, in assessments of memory. Topol rightly points out that the study requires replicating. It should also, if possible, look at a much wider range of ethnicities and ages. Unfortunately, the current study tells us little about 'Long-Covid' which may have a very different genesis.