COVID-19 may leave some people with lasting memory problems long after their infection has cleared, new research has found, with the findings particularly pronounced among those who suffered from the earliest variants of the virus.
COVID-19 is known for its respiratory symptoms. But we are increasingly learning that SARS-CoV-2—the virus that causes the infection—can affect our brains too. Brain fog, cognitive deficits, and loss of smell and taste are commonly reported symptoms of the virus and some report these neurological symptoms long after the initial infection has subsided.
Scientists aren't entirely sure why the virus causes these symptoms, although lab-based studies have shown that the virus can disrupt the protective barrier that surrounds our brains and prevents foreign substances, like viruses, from entering. Research has also shown that the virus appears to affect the ability of our brain cells to communicate with each other, producing either too much or too little of key signaling molecules in the brain.
In a new study, published in the journal eClinicalMedicine, researchers from Imperial College London, King's College London and University College London Hospital in the United Kingdom set out to investigate the persistence of these cognitive symptoms even after milder COVID-19 infections.
In the study, 18 consenting unvaccinated volunteers with no prior exposure to SARS-CoV-2 were intentionally infected with the virus and monitored regularly over a 360-day period. Their cognitive function was measured at different points throughout the study and compared to what it had been before they were infected. They were also compared against 16 volunteers who were not infected with the virus.
This type of study is called a human challenge study and offer valuable insights into the onset of diseases and how they develop in a controlled medical environment.
"This is the first and probably will be the only Human Challenge Study to be conducted with Wildtype SarS-CoV-2 in people who were unvaccinated and who had not previously had the virus," the study's lead author Adam Hampshire, a professor of cognitive and computational neuroscience at King's College London and visiting professor at Imperial College London's Department of Brain Sciences, told Newsweek.
He added: "It also is the first study to apply detailed and sensitive assessments of cognitive performance from pre to post infection under controlled conditions. In this respect, the study provides unique insights into the changes that occurred in cognitive and memory function amongst those who had mild COVID-19 illness early in the pandemic."
During the study, the volunteers who were infected showed statistically significant reductions in cognitive and memory functions compared to those who did not receive the virus. These symptoms did not emerge right away but lasted for at least a year after the initial infection. This aligns with previous research from Hampshire's lab that sampled data from over 100,000 adults.
"Our previous research has shown that cognitive effects were the most pronounced for people who were ill with early virus variants, those who had persistent symptoms and those who were hospitalized," Hampshire said.
However, in the recent study, these long-lasting cognitive impacts were even seen in those who experienced milder symptoms (although it is worth noting that this may not be the case with newer variants of the virus).
So, how does the virus cause these cognitive impairments? Well, we still don't know for sure, but Hampshire said that those who had been infected with the virus showed an increase in a protein in the brain that is often associated with a brain injury.
"Future research should examine the biological mechanisms that mediate this relationship, determine how they differ to those observed for other respiratory infections, and explore whether targeted interventions can normalize these memory and executive processes," the researchers write in their study.
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References
Proust, A., Queval, C. J., Harvey, R., Adams, L., Bennett, M., & Wilkinson, R. J. (2023). Differential effects of SARS-CoV-2 variants on central nervous system cells and blood-brain barrier functions. Journal of neuroinflammation, https://doi.org/10.1186/s12974-023-02861-3
Trender, W. et al. (2024) Changes in memory and cognition during the SARS-CoV-2 human challenge study. eClinicalMedicine, https://doi.org/10.1016/j.eclinm.2024.102842
Hampshire, A., Azor, A., Atchison, C., Trender, W., Hellyer, P. J., Giunchiglia, V., Husain, M., Cooke, G. S., Cooper, E., Lound, A., Donnelly, C. A., Chadeau-Hyam, M., Ward, H., & Elliott, P. (2024). Cognition and Memory after Covid-19 in a Large Community Sample. The New England journal of medicine. https://doi.org/10.1056/NEJMoa2311330
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