The condition often referred to as 'brain fog' in people with long COVID could have a similar effect to ageing a decade, according to UK researchers, who called for more work to understand why this was the case and what could be done to help.
Cognitive impairment has been reported after many types of infection, including SARS-CoV-2, highlighted the team from King's College London (KCL), but it was unclear whether deficits following SARS-CoV-2 improve over time. They underlined that to date, studies had focused on hospitalised individuals with up to a year follow-up, but that the presence, magnitude, persistence, and correlations of effects in community-based cases remained "relatively unexplored".
The prospective cohort study, published in the journal eClinicalMedicine, set out to explore the impact of long COVID on thinking and memory skills. Researchers assessed cognitive performance — working memory, attention, reasoning, and motor control — of participants from the UK COVID Symptom Study Biobank in the first round between July and August, 2021, and the second, between April and June, 2022. Round one comprised 3335 individuals with and without SARS-CoV-2 infection and varying symptom duration, while data was available on 1768 individuals who also completed round two.
The effect of COVID-19 exposures on cognitive accuracy and reaction time scores were estimated, and the role of ongoing symptoms after SARS-CoV-2 infection was examined.
Claire Steves, professor of ageing and health at KCL, and a corresponding study author, said investigators "used sensitive tests to measure speed and accuracy across a range of brain challenges."
Decreased Cognitive Accuracy
The researchers found that at round 1, individuals with previous positive SARS-CoV-2 tests had lower cognitive accuracy than negative controls.
Cognitive deficits were largest for individuals with "longer symptom durations, ongoing symptoms, and/or more severe infection", identified the researchers. Following SARS-CoV-2 infection, these deficits were detectable nearly 2 years post infection. However, no such deficits were detected in individuals who reported full recovery from COVID-19, the authors said.
"Deficits were largest for positive individuals with ≥12 weeks of symptoms," the researchers reported, with effects "comparable to hospital presentation during illness and 10 years age difference in the whole study population," they alerted.
Dr Nathan Cheetham, a senior postdoctoral data scientist at KCL, who led the research team, 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."
Stratification by self-reported recovery revealed that deficits were only detectable in SARS-CoV-2 positive individuals who did not feel they had recovered from COVID-19, whereas individuals who reported full recovery showed no deficits.
Longitudinal analysis showed no evidence of cognitive change over time, which suggested that cognitive deficits for affected individuals "persisted" at almost 2 years since initial infection.
Professor Steves emphasised that the study showed that some individuals had "measurable changes" in cognitive function after COVID-19 going on for "nearly two years".
"The deficits in composite task accuracy scores were comparable in scale to the effect of presentation to hospital during illness, an increase in age of approximately 10 years, or exhibiting mild or moderate symptoms of psychological distress, but smaller than other effects such as lower educational attainment or above threshold fatigue level," according to the authors.
Lives "Continue to be Impacted by COVID-19"
The researchers found "no evidence" of an effect of SARS-CoV-2 infection on average reaction time during tasks. This, they emphasised, was "reassuring" given the importance of processing speed within cognition and extensive relationships with outcomes such as frailty, dementia, and later mortality.
However, the scale of the deficits identified in the study may have "detrimental impacts" on quality-of-life and daily functioning at an individual level, as well as socio-economic impacts on society more broadly due to both a reduced capacity to work and an increased need for support, the authors cautioned.
They called for further work to monitor and develop understanding of recovery mechanisms for those with ongoing symptoms.
"The fact remains that two years on from their first infection, some people don't feel fully recovered and their lives continue to be impacted by the long-term effects of the coronavirus," commented Professor Steves, who said there was a need for "more work to understand why this is the case and what can be done to help".
Funding for the study was provided by the Chronic Disease Research Foundation, Wellcome Trust, National Institute for Health and Care Research, Medical Research Council, British Heart Foundation, Alzheimer's Society, European Union, COVID-19 Driver Relief Fund, and the French National Research Agency.