Long Covid has a measurable impact on memory and cognition a year or more after infection, a large UK study has reported.
A series of cognitive tests done on 112,000 people who took part in the REACT study found larger deficits in people who were hospitalised, who had ongoing symptoms for a long time, or who were infected with earlier variants of the virus.
Reporting the findings in the New England Journal of Medicine, researchers from Imperial College London said it would be important to measure long-term clinical and cognitive consequences for patients with ‘brain fog’ as a result of long Covid.
Those taking part in the study were asked to do an online cognitive assessment which included tasks that can detect subtle changes in memory, reasoning, executive function, attention and impulsivity.
Results were compared across people who had differing severity of Covid infection and length of persistent symptoms and also controlled for age, demographics and pre-existing conditions.
Small deficits were apparent a year or more after infection even in those whose illness had been of a relatively short duration, the team found.
But a larger impact was seen in those whose symptoms lasted 12 weeks or more and those who had longer lasting symptoms that had resolved by the time they did the test still showed small deficits similar in size to people who had a shorter illness, they added.
They found the risk of having more severe cognitive problems was almost twice as high in those who had Covid-19 compared to those who did not, and three times as high in those who were hospitalised.
The impact was seen in several areas of cognition tested for but most notably in memory, particularly around the ability to remember pictures of objects that were viewed a few minutes earlier, which could be due to problems forming new memories.
People also showed small deficits in some executive function tasks requiring spatial planning or verbal reasoning.
National surveys have identified more than 1 million people in the UK report Covid-19 symptoms persisting more than 12 weeks, with over 750,000 reporting ongoing symptoms more than two years after infection.
Study lead Professor Adam Hampshire, professor in restorative neurosciences said: ‘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.
‘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. We also found that people were likely affected in different ways depending on factors such as illness duration, virus variant and hospitalisation.’
Professor Paul Elliott, co-author and director of the REACT study said 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
‘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.’
Commenting on the results, Dr Michael Zandi, neurologist and researcher at University College London, said: ‘The biological mechanisms underlying these findings are likely multiple, remain unclear and deserve detailed longitudinal study and therapeutic trials.’
Dr Maxime Taquet, a clinical fellow in psychiatry at the University of Oxford said that cognitive deficits in people with long Covid was an important public health problem but the magnitude of the problem had been largely unknown.
‘This important and well-conducted study provides the first accurate quantification of the scale of cognitive deficits in people who had Covid-19.’
But she added there were still questions to answer. ‘Do these cognitive problems persist or improve in the years after infection. What is their biological explanation. How does it affect people’s everyday life and their ability to work,’ she said.
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