Severe COVID results in cognitive impairment similar to that sustained between 50 and 70 years of age and is the equivalent of losing ten IQ points, our latest research shows. The effects are still detectable more than six months after the acute illness, and recovery is, at best, gradual.
There is growing evidence that COVID 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.
In the UK, a study found that around one in seven people surveyed reported having symptoms that included cognitive difficulties 12 weeks after a positive COVID test. And a recent brain imaging study found that even mild COVID can cause the brain to shrink. Only 15 of the 401 people in the study had been hospitalised.
Incidental findings from a large citizen-science project (the Great British Intelligence Test) also showed that mild cases can lead to persistent cognitive symptoms. However, these problems appear to increase with the severity of the illness. Indeed, it has been independently shown that between a third and three-quarters of hospitalised patients report suffering cognitive symptoms three to six months later.
The magnitude of these problems, and the mechanisms that are responsible, remain unclear. Even before the pandemic, it was known that a third of people who have an episode of illness that requires ICU admission show objective cognitive deficits six months after admission.
This is thought to be a consequence of the inflammatory response associated with critical illness, and the cognitive deficits seen in COVID could well be a similar phenomenon. Yet there is evidence that SARS-CoV-2, the virus that causes COVID, can infect brain cells. We cannot exclude direct viral infection of the brain.
Other factors, such as hypoxia (low oxygen levels in the blood), may also have a role. It was also unclear whether the pervasive problems with psychological health reported after COVID were part of the same problem as the objective cognitive deficits, or represented a different phenomenon.
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