A new study from the United Kingdom provides greater clarity on how SARS-CoV-2 infection can affect cognition and memory, including novel data on how long brain fog may last after the illness resolves and which cognitive functions are most vulnerable.
In a large community sample, researchers found that on average, people who had recovered from COVID-19 showed small cognitive deficits equivalent to a 3-point loss in IQ for up to 1 year or more after recovering from the acute illness compared with peers who never had COVID-19.
However, people who had more severe cases, requiring treatment in a hospital intensive care unit, had cognitive deficits equivalent to a 9-point drop in IQ.
“People with ongoing persistent symptoms, indicative of long COVID, had larger cognitive deficits than people whose symptoms had resolved,” first author Adam Hampshire, PhD, with Imperial College London, London, England, told this news organization.
The largest deficits among cognitive tasks were in memory, reasoning, and executive function, he added.
“That is, people who had had COVID-19 were both slower and less accurate when performing tasks that measure those abilities,” Dr. Hampshire said. “The group with the largest cognitive deficits were patients who had been in intensive care for COVID-19.”
The study was published online in The New England Journal of Medicine.
Lingering Brain Fog
Cognitive symptoms after SARS-CoV-2 infection are well recognized, but whether objectively measurable cognitive deficits exist and how long they persist remains unclear.
To investigate, researchers invited 800,000 adults from the REACT study of SARS-CoV-2 transmission in England to complete an online assessment for cognitive function with eight domains.
Altogether, 141,583 participants started the cognitive battery by completing at least one task, and 112,964 completed all eight tasks.
The researchers estimated global cognitive scores among participants who had been previously infected with SARS-CoV-2 with symptoms that persisted for at least 12 weeks, whether or not resolved, and among uninfected participants.
Compared with uninfected adults, those who had COVID-19 that resolved had a small cognitive deficit, corresponding to a 3-point loss in IQ, the researchers found.
Adults with unresolved persistent COVID-19 symptoms had the equivalent of a 6-point loss in IQ, and those who had been admitted to the intensive care unit had the equivalent of a 9-point loss in IQ, in line with previous findings of cognitive deficits in patients hospitalized in a critical care unit, the researchers report.
Larger cognitive deficits were evident in adults infected early in the pandemic by the original SARS-CoV-2 virus or the B.1.1.7 variant, whereas peers infected later in the pandemic (eg., in the Omicron period), showed smaller cognitive deficits. This finding is in line with other studies suggesting that the association between COVID-19–associated cognitive deficits attenuated as the pandemic progressed, the researchers noted.
They also found that people who had COVID-19 after receiving two or more vaccinations showed better cognitive performance compared with those who had not been vaccinated.
The memory, reasoning, and executive function tasks were among the most sensitive to COVID-19–related cognitive differences and performance on these tasks differed according to illness duration and hospitalization.
Dr. Hampshire said that more research is needed to determine whether the cognitive deficits resolve with time.
“The implications of longer-term persistence of cognitive deficits and their clinical relevance remain unclear and warrant ongoing surveillance,” he said.