Scientists from the University of Cambridge and elsewhere found that cognitive impairment as a result of severe COVID-19 is similar to that sustained between 50 and 70 years of age and is the equivalent of losing 10 IQ points.
The findings suggest the effects are still detectable more than six months after the acute illness, and that any recovery is at best gradual.
The research is published in the journal eClinicalMedicine and was conducted by Professor David Menon et al.
There is growing evidence that COVID-19 can cause lasting cognitive and mental health problems, with recovered patients reporting symptoms including fatigue, ‘brain fog’, problems recalling words, sleep disturbances, anxiety and even post-traumatic stress disorder (PTSD) months after infection.
While even mild cases can lead to persistent cognitive symptoms, between a third and three-quarters of hospitalized patients report still suffering cognitive symptoms three to six months later.
In the study, the team analyzed data from 46 individuals who received in-hospital care, on the ward or intensive care unit, for COVID-19.
16 patients were put on mechanical ventilation during their stay in the hospital. All the patients were admitted between March and July 2020.
The team found the COVID-19 survivors were less accurate and with slower response times than the matched control population—and these deficits were still detectable when the patients were followed up six months later.
The effects were strongest for those who required mechanical ventilation.
By comparing the patients to 66,008 members of the general public, the researchers estimate that the magnitude of cognitive loss is similar on average to that sustained with 20 years aging, between 50 and 70 years of age, and that this is equivalent to losing 10 IQ points.
Survivors scored particularly poorly on tasks such as verbal analogical reasoning, a finding that supports the commonly-reported problem of difficulty finding words.
They also showed slower processing speeds, responsible for attention, complex problem-solving and working memory, among other functions.
The team says cognitive impairment is common to a wide range of neurological disorders, including dementia, and even routine aging, but the patterns in the study —the cognitive ‘fingerprint’ of COVID-19—was distinct from all of these.
While it is now well established that people who have recovered from severe COVID-19 illness can have a broad spectrum of symptoms of poor mental health—depression, anxiety, post-traumatic stress, low motivation, fatigue, low mood, and disturbed sleep—the team found that acute illness severity was better at predicting the cognitive deficits.
The patients’ scores and reaction times began to improve over time, but the researchers say that any recovery in cognitive faculties was at best gradual and likely to be influenced by a number of factors including illness severity and its neurological or psychological impacts.
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