People who have previously been infected with COVID-19 and recovered may have significantly reduced intelligence, suggests a new study published in EClinicalMedicine. The research adds to a growing list of concerns about the long-lasting impact of COVID-19 on the body and brain, and suggests that long-term studies should begin immediately to assess just how severe the effects could be.
Conducted by Imperial College London, the study involved 81,337 people who took part in an online assessment as part of the Great British Intelligence Test. This is a clinically validated cognitive test that involves a series of short brain challenges, as well as a questionnaire to fill out. You can take the test yourself here.
Of these 81,337 people, some had previously had COVID-19 infection confirmed through testing but had not been hospitalized (N=326), and some had been hospitalized with severe COVID-19 (N=192). The results were taken to assess their cognitive ability, which was then compared to the overall sample to identify any lingering effects of COVID-19 infection.
After controlling for factors including age, sex, education, first language, and handedness amongst others the researchers discovered a decrease in cognitive deficits in those that had previously contracted COVID-19, which was further exacerbated by more severe cases. Those with respiratory symptoms scored more poorly on the test than those without respiratory issues, and there was a marked increase in deficits with those that went to hospital for their symptoms.
While there may be many reasons for these results, the researchers extensively explored possible confounding factors, including pre-existing conditions and any ongoing COVID-19 symptoms, and found that controlling for these factors left the results relatively unchanged.
Lead researcher and scholar in long COVID Adam Hampshire posted a thread on twitter summarizing the findings.
“This isn't just about long covid – this compares people who had had covid with those who hadn't, regardless of ongoing symptoms. Most people who had had covid reported being recovered, but about 25% with confirmed covid reported ongoing symptoms (I.e., long covid),” tweeted Professor Christina Pagel, director of University College London’s Clinical Operational Unit, in another thread explaining the results.
“The cognitive deficits remained whether ongoing symptoms were there or not, and did not depend on time since covid either. This seems to suggest it is a long-lasting effect. It also doesn't depend on pre-existing health problems.”
The deficits are not minor either – those who had previously been on a ventilator had a deficit of 0.47, while those without a ventilator had a deficit of 0.27. To put that in perspective, the average deficit experienced by stroke patients is 0.24 (the higher the deficit, the more cognitive issues the patient has). Furthermore, the deficit was even larger than the average person that reported learning difficulties (0.38).
The most pronounced deficits in COVID-19 patients were those of reasoning, problem-solving, spatial planning, and target detection, aligning with previous reports of "brain fog".
As with any self-reported data, interpreting the results needs to be carried out with caution. Sampling bias could play a role (although the authors did their best to mitigate this), and there are many other factors that may play into neurological assessments. However, the study appears to highlight a significant and lasting impact on patients of all ages, and calls for substantial more investigation of those that now live with long COVID.