Long-COVID patients performed worse on cognitive tests for up to 2 years

Older forgetful man

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Cognitive deficits equivalent to a 10-year increase in age were more common in COVID patients who still had symptoms 3 months or more after infection, according to a study published late last week in eClinicalMedicine.

A King's College London-led team evaluated performance on 12 tasks that tested working memory, attention, reasoning, processing speed, and motor control among previously infected participants and never-infected controls with and without persistent symptoms (eg, psychological distress, fatigue, functional impairment) in the UK COVID Symptom Study Biobank.

Round 1 of testing took place from July 12 to August 27, 2021, and round 2 occurred 9 months later  (April 28 to June 21, 2022). A total of 3,335 participants completed round 1, and 1,768 also completed round 2. Participants were, on average, 57.5 years old, 81.2% were women, 96.5% were White, and 34.5% lived in lower-deprivation neighborhoods.

Delayed recall of objects

During round 1, previously infected participants had lower accuracy on online cognitive tests (β, −0.14 standard deviations [SD]) than controls. The effects were greatest for previously infected participants who had symptoms for 3 months or more (β, −0.22 SDs) and those who were hospitalized (β, −0.31 SDs) and were equivalent to a 10-year age increase (60 to 70 years vs 50 to 60 years; β, −0.21 SDs) in the entire study cohort.

Test scores didn't improve significantly between the two rounds, which took 2 years to complete. Effect sizes and/or strength of associations in infected participants were generally lower than in the second than in the first round. Cognitive deficits were detectable only in participants who said they weren't fully recovered from COVID-19.

Tasks with the most consistent evidence of lower accuracy in COVID-19 participants included those that measured episodic visual memory, those that tested immediate and delayed recall of objects, and those that evaluated visual attention and processing speed in the 'target detection' tasks, in which participants found and chose target shapes from an evolving grid of shapes.

This study shows the need to monitor those people whose brain function is most affected by COVID-19, to see how their cognitive symptoms continue to develop and provide support towards recovery.

Evidence of cognitive impairment at an individual task level among infected groups varied more during other tasks that tested working memory, spatial planning and mental manipulation, motor control, and semantic reasoning.

Ongoing symptoms may be better predictor

There were important differences between the two rounds in terms of symptom persistence. "At initial testing in mid-2021, cognitive deficits are not found for individuals who self-report as feeling recovered from COVID-19, even for those with longest symptom duration," the study authors wrote. "In follow-up testing in mid-2022, we find that deficits appear persistent for those with earlier infections and ongoing symptoms, consistent with previous smaller studies."

The results show that for people who had long-term symptoms after COVID-19 infection, the virus's effects on mental tasks may still be detectable an average 2 years later, lead author Nathan Cheetham, PhD, said in a King's College London news release.  

However, the result that COVID had no effect on performance in our tests for people who felt fully recovered, even if theyd had symptoms for several months and could be considered as experiencing long COVID,was good news," he said. "This study shows the need to monitor those people whose brain function is most affected by COVID-19, to see how their cognitive symptoms continue to develop and provide support towards recovery.”

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