Even mild cases of COVID cause significant, measurable cognitive deficits compared to those never infected with the virus, according to one of the largest studies of its type. COVID brain fog is real, and it can sap up to six IQ points for at least a year.
“The potential long-term effects of COVID-19 on cognitive function have been a concern for the public, healthcare professionals, and policymakers, but until now it has been difficult to objectively measure them in a large population sample,” explained Adam Hampshire, first author on the newly published study.
The research comes out of one of the world’s largest and longest running COVID studies, dubbed REACT (Real-Time Assessment of Community Transmission). The project, which kicked off in April 2020, follows nearly three million people in England. The goal is to better understand who is suffering from long-term symptoms with COVID and what those symptoms actually are.
This particular REACT investigation homed in on around 112,000 people who completed online assessments uniquely developed to measure cognitive domains that have been known to be affected by COVID. Each participant also supplied COVID infection history allowing the researchers to compare cognitive findings with symptom duration and severity.
Between three and four percent of the total cohort qualified as suffering from long COVID, reporting symptoms lasting more than 12 weeks. The majority of that long COVID group were still experiencing symptoms up to one year later.
Of those long COVID patients the researchers suggest their cognitive assessments showed deficits that correlated with a drop in about six IQ points compared to those with no history of infection. The deficits were primarily detected in cognitive domains associated with memory, spatial planning and verbal reasoning.
“By using our online platform to measure multiple aspects of cognition and memory at large scale, we were able to detect small but measurable deficits in cognitive task performance,” said Hampshire. “We also found that people were likely affected in different ways depending on factors such as illness duration, virus variant and hospitalisation.”
More interestingly, the researchers found small but statistically significant differences in cognition between people who recovered quickly from short bouts of COVID and people with no history of infection. The cognitive assessments correlated with differences of about three IQ points.
While a drop in three IQ points from a mild, passing COVID infection would not be particularly noticeable in an average person’s day-to-day life, experts commenting on the study suggest these kinds of deficits may be relevant on a population level, considering the scale of the pandemic.
“Even if cognitive deficits after COVID-19 are of small magnitude on average, a substantial minority of people have more significant deficits which are likely to affect their ability to work and function,” said Maxime Taquet, a psychiatrist from the University of Oxford who did not work on the new study. “Given the scale of the pandemic and the number of people affected, this is particularly worrisome.”
In a commentary on the study published in the New England Journal of Medicine, long-COVID experts Ziyad Al-Aly and Clifford Rosen called the findings concerning. They noted that the pandemic has impacted millions around the world and even small cognitive deficits from the virus could have larger long-term implications.
“For example, what are the functional implications of a three-point loss in IQ?” the pair asked in their commentary. “Whether one group of persons is affected more severely than others is not clear. Whether these cognitive deficits persist or resolve along with predictors and trajectory of recovery should be investigated. Will COVID-19–associated cognitive deficits confer a predisposition to a higher risk of Alzheimer’s disease or other forms of dementia later in life?”
However, the findings are not all bad news. Participants with long-COVID symptoms that resolved over time showed only small cognitive deficits that resembled what was seen in people with short, mild illness. Paul Elliot, senior author on the study, said this indicates the potential for long-COVID patients to get better over time.
“Furthermore, the cognitive impact of COVID-19 appears to have reduced since the early stages of the pandemic, with fewer people having persistent illness, and cognition being less affected amongst those that were infected during the time when Omicron was the dominant strain,” Elliot added. “However, given the large numbers of people who were infected, it will be important to continue to monitor the long-term clinical and cognitive consequences of the COVID-19 pandemic.”
The study was published in The New England Journal of Medicine.
Source: Imperial College London