People experiencing long 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 summer 2022, revealed that Covid-19 may have an impact on cognitive and memory abilities that lasts a year or more after infection. People with unresolved symptoms that had persisted for more than 12 weeks had more significant deficits in performance on tasks involving memory, reasoning and executive function. Scientist said this 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’s not been at all clear what brain fog actually is. As a symptom it’s been reported on quite extensively, but what our study shows is that brain fog can correlate with objectively measurable deficits. That is quite an important finding.”
Last year the Office for National Statistics estimated about 2 million people in the UK were experiencing self-reported long Covid. Previous Imperial College analysis found tens of thousands of people in England may have symptoms that had lasted a year or more after infection.
The latest study recruited more than 140,000 participants from the original React cohort, which launched in April 2020 as one of the world’s largest and most comprehensive Covid surveillance studies. Between August and September 2022, participants were given online cognitive tests designed to test memory, attention, reasoning and other aspects of brain function.
About 3.5% of the cohort had experienced symptoms that persisted beyond 12 weeks, and of these about two-thirds still had symptoms at the time of the assessment.
The analysis found small deficits that were still detectable a year or more after infection, for those who had been infected and no longer had symptoms. The difference in test scores between those who had been infected and those who had not was equivalent to about three IQ points, had they been given an IQ test.
For an individual, this size of change is unlikely to be noticeable, scientists said, although some may have experienced more pronounced effects.
Those patients with unresolved symptoms that had persisted for more than 12 weeks were found to have a larger 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 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. Given the scale of the pandemic and the number of people affected, this is particularly worrisome.”
More encouragingly, those who had longer-lasting symptoms that had resolved showed comparable deficits to those who had experienced mild, short duration 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 that had resolved may expect to experience some improvement in their cognitive functions to similar levels as those who experienced short illness.”
They were larger differences for people who had unresolved symptoms lasting 12 weeks or more (consistent with long Covid) and those who had been to hospital for their illness, who had the most noticeable deficits and ones that extended to a broader range of cognitive functions. The differences were also bigger for those who were 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.
