Long-term Covid can lead to measurable cognitive decline, especially in the ability to remember, reason and plan, a major new study suggests.
Cognitive tests of nearly 113,000 people in England found that those with persistent post-Covid symptoms scored the equivalent of 6 IQ points lower than people who had never been infected with the coronavirus, according to the study published Wednesday in The New England Journal of Medicine. .
People who had been infected and no longer had symptoms also scored slightly lower than people who had never been infected, by 3 IQ points, even if they had been ill for a short time.
The differences in cognitive scores were relatively small, and the neurologists cautioned that the results did not imply that the coronavirus infection or long-term exposure to Covid caused profound deficits in thinking and functioning. But experts said the findings are important because they provide figures for the brain fog, focus and memory problems that plague many people with long-term Covid.
“These emerging and converging findings generally underscore that yes, there is cognitive impairment in long-term Covid survivors — it’s a real phenomenon,” said James C. Jackson, a neuropsychologist at Vanderbilt Medical Center, who was not involved in the study.
He and other experts noted that the results were consistent with smaller studies that have found signs of cognitive decline.
The new study also found reason for optimism, suggesting that if people’s long-term Covid symptoms subside, the associated cognitive impairment might too: People who had experienced long-term Covid symptoms for months and eventually recovered had cognitive outcomes similar to those who had experienced a quick recovery , the study found.
On a standard IQ scale, people who score between 85 and 115 are considered of average intelligence. The standard deviation is about 15 points, so a shift of 3 points is not usually considered significant, and a shift of even 6 points may not be consequential, experts said.
“The point is: Are people able to function at their usual capacity in whatever they’re doing? And that’s not really answered by 3 points more or less,” said Dr. Igor Koralnik, chief of neuro-infectious diseases and global neurology at Northwestern Medicine in Chicago, who was not involved in the study.
He added: “Determining X scores on an IQ scale is less important than people’s perception of their cognitive difficulties.”
However, Dr Jackson, the author of a lengthy book on Covid called Clearing the Fog, said that while cognitive tests like the one in the study “pick up relatively mild deficits”, even subtle difficulties can matter for some people . For example, he said, “if you’re an engineer and you have a little decline in executive function, that’s a problem.”
The study, led by researchers at Imperial College London, involved 112,964 adults who completed an online cognitive assessment during the last five months of 2022. About 46,000 of them, or 41 percent, said they had never had Covid. Another 46,000 people infected with the coronavirus said their illness lasted less than four weeks.
About 3,200 people had post-Covid symptoms that lasted four to 12 weeks after their infection, and about 3,900 people had symptoms beyond 12 weeks, including some that lasted a year or more. Of these, 2,580 people still had post-Covid symptoms at the time they took the cognitive test.
The researchers noted that they relied on self-reported symptoms, rather than long-standing Covid diagnoses, and that the requirements to take a cognitive test may have meant that study participants were not the most severely impaired.
