LONDON: People who have recovered from COVID-19 may face problems in cognitive tasks such as thinking and attention, according to a study of over 80,000 individuals.
The research, published in the journal EClinicalMedicine, found that those with more severe COVID-19 symptoms scored lower on an online series of tests, with performance on reasoning and problem-solving tasks being most affected.
Further analysis of the data indicated that those who received mechanical ventilation to help them breathe while in the hospital had the greatest impairment on cognitive tasks.
"Our study adds to an increasing body of research that is looking at different aspects of how COVID-19 might be impacting the brain and brain function," said study first author Adam Hampshire from Imperial College London in the UK.
"This research is all converging to indicate that there are some important effects of COVID-19 on the brain that need further investigation," Hampshire said.
The online tests, developed by researchers at Imperial College London, had been opened up to the general public just before the pandemic.
In early 2020, the team, including researchers from Kings College London and University of Cambridge in the UK, extended the questionnaires to gather information on SARS-CoV-2 infection, the symptoms experienced and the need for hospitalisation.
Out of the 81,337 who provided complete data, 12,689 people suspected they had COVID-19.
Participants reported a range of severity of illness, with 3,559 participants experiencing respiratory symptoms whilst still being able to stay at home.
Nearly 200 were hospitalised and about a quarter of these required mechanical ventilation.
The time since illness onset was around 1-6 months, meaning the study could not draw any definitive conclusions about whether these effects on cognition were long-lasting.
The study found a relationship between deficits in overall cognitive performance and severity of respiratory symptoms experienced.
The researchers also found that not all areas of thinking ability correlated in the same way with COVID-19 illness and that some abilities were spared, which included emotional discrimination and working memory.
In comparison, "executive" tasks that required skills in reasoning and problem solving seemed to show the greatest deficit, they said.
To understand the size of the deficits, the authors compared the pattern of scores on the tests to cognitive changes that occur for other reasons.
The effects in those hospitalised with mechanical ventilation were similar to the average cognitive decline seen over a period of ten years of aging and equivalent to a seven-point difference in IQ.
The team, which also included researchers from the University of Chicago, US, carried out a series of checks to ensure these cognitive deficits were associated with COVID-19 and not explicable by other variables.
These included separating out those who had a confirmed positive test for SARS-CoV-2 and demonstrating that the cognitive deficits were indeed greater in those with positive tests.
Further checks suggested the results were not due to a minority with pre-existing conditions or on-going symptoms of COVID-19.
Analysis also indicated that it was unlikely that the results could be explained by the fact that those who contracted more severe COVID-19 disease were less cognitively able before they were ill.
The researchers noted that it would be valuable to bring together brain imaging and cognitive tests with other information on mental health and everyday function, ideally in studies that track people's trajectories for months or even years.
To really know what the long-term effects are for people will require people to be followed up over time, they added.