People who experience prolonged Covid have measurable memory and cognitive deficits equivalent to a difference of about six IQ points, a study suggests.
The study, which assessed more than 140,000 people in the summer of 2022, revealed that Covid-19 can have an impact on cognitive and memory abilities that last a year or more after infection. People with unresolved symptoms that persisted for more than 12 weeks had more significant deficits in performance on tasks involving memory, reasoning and executive function. Scientist said it showed that “brain fog” had a quantifiable impact.
Prof Adam Hampshire, a cognitive neuroscientist at Imperial College London and first author of the study, said: “It was not at all clear what brain fog actually was. As a symptom it has been reported quite extensively, but what our study shows is that brain fog can correlate with objectively measurable deficits. This is quite an important finding.”
Last year the Office for National Statistics estimated about 2 million people in the UK self-reported prolonged Covid experience. Previous Imperial College analysis found tens of thousands of people in England may have symptoms lasting a year or more after infection.
The latest study recruited more than 140,000 participants from the original React cohort, which was launched in April 2020 as one of the world’s largest and most comprehensive Covid surveillance studies. Between August and September 2022, participants received online cognitive tests designed to test memory, attention, reasoning and other aspects of brain function.
About 3.5% of the group experienced symptoms lasting longer than 12 weeks, and of these, about two-thirds still had symptoms at the time of assessment.
The analysis found small deficits that were still detectable a year or more after infection for those who were infected and no longer had symptoms. The difference in test scores between those who were infected and those who were not was equivalent to about three IQ points, if given an IQ test.
For an individual, this magnitude of change is unlikely to be noticeable, scientists said, although some may have experienced more pronounced effects.
Patients with unresolved symptoms lasting longer than 12 weeks were found to have a greater deficit, equivalent to six IQ points.
Dr Maxime Taquet, a psychiatrist and researcher at the University of Oxford who was not involved in the study, said: “Even if cognitive deficits after Covid-19 are on average of small magnitude, a significant minority of people have more significant deficits which is likely to affect their ability to work and function. Given the scale of the pandemic and the number of people affected, this is of particular concern.”
More encouragingly, those who had longer-lasting symptoms that resolved showed comparable deficits than those who experienced mild, short-term illness.
Prof Paul Elliott, a senior author and director of the React programme, from Imperial College London, said: “It is reassuring that people with persistent symptoms after Covid-19 who have resolved can expect to see some improvement in experience their cognitive functions to similar levels as those who experienced brief illness.”
There were greater differences for people who had unresolved symptoms lasting 12 weeks or longer (consistent with long Covid) and those who were in hospital for their illness, who had the most noticeable deficits and one that extended to ‘ a greater range of cognitive functions. The differences were also greater for those infected with one of the early variants of the virus, but it was not possible to say whether this was due to the introduction of vaccines and better treatment as the pandemic unfolded.
The findings are published in the New England Journal of Medicine.
