July 30, 2021 — Infection from COVID-19 may have a substantial negative effect on intelligence, according to a new large-scale study from the United Kingdom, findings that are consistent with reports of “brain fog” among long-haul COVID-19 patients.
Researchers analyzed data from 81,337 people who took the Great British Intelligence Test in 2020. Of those, about 13,000 reported they had contracted COVID-19, and 275 of those had completed the test before and after infection.
Those who had previously had the coronavirus found it harder to complete tasks related to reasoning, problem-solving, and spatial planning, the authors said. Researchers controlled for age, education, and overall mood.
“These results accord with reports of long-COVID, where ‘brain fog,’ trouble concentrating, and difficulty finding the correct words are common,” the authors wrote. “Recovery from COVID-19 infection may be associated with particularly pronounced problems in aspects of higher cognitive or ‘executive’ function.”
Working memory span and emotional processing did not seem to be affected.
How bad the cognitive decline was appeared to be linked to how serious the infection was. Researchers said those who had been placed on a ventilator while ill showed the most substantial effects. On average, their score dropped 7 IQ points.
“The scale of the observed deficit was not insubstantial,” the authors wrote. But they said brain imaging is needed before firm conclusions can be drawn.
“It is important to be cautious in inferring a neurobiological or psychological basis of the observed deficits without brain imaging data, although the assessment tasks used here have been shown to map to different networks within the human brain in terms of normal functional activity and connectivity as well as structural network damage,” they wrote.
The researchers speculate that high fever and respiratory problems could have contributed to the cognitive decline. But those symptoms had long dissipated for most people in the study — the authors noted only 4.8% of them reported lingering symptoms.
The study provides insight into one part of post-COVID — a condition that has been closely tracked by the CDC. According to the agency, long-haul COVID-19 can include a range of lingering symptoms several months after infection, including shortness of breath, headache, joint or muscle pain, dizziness, and a hard time thinking or concentrating, otherwise known as “brain fog.”