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Contracting Covid makes people less intelligent and severe infections lower IQ the most, a study suggests.
Britons who avoided the disease generally performed better on intelligence tests, while those who ended up in hospital performed the worst.
But it is believed that even those who suffered only a mild illness are likely to have suffered deterioration in their cognitive abilities.
Scientists at Imperial College London analyzed data from more than 112,000 volunteers who underwent Covid tests during the pandemic.
The analysis revealed that those who entered intensive care with Covid scored around nine IQ points lower on average than those who avoided infection.
Those who reported having had long Covid (persistent symptoms such as “mental confusion”) scored six points less and those with only a mild infection two points less.
Professor Adam Hampshire, lead author of the study published in The Lancet medical journal, tried to match people as closely as possible when comparing the groups in a bid to take other factors into account.
Closer examination found lasting cognitive impacts, even in people infected a year or more earlier.
The original Covid strain was associated with a greater drop in IQ, while there were only marginal differences with Omicron. Vaccination also appeared to have a protective effect.
Professor Hampshire said the implications of the figures are “quite scary”.
The participants had enrolled in Imperial College’s React study. Dr. Taquet said the results should be interpreted with caution since the study did not compare the same person before and after infection.
Professor Benedict Michael, director of the infection neuroscience laboratory at the University of Liverpool, said: “There is clearly a very severely affected group.”
But he added: “I have yet to see convincing evidence that the vast majority of the population has lost X IQ points.”
Separate studies looking at brain scans done before and after the pandemic suggest that Covid infection can have an impact, even on those who had not been hospitalized.
Professor Michael said it did not appear to be the virus that was infecting the brain, but rather a secondary consequence of an infection elsewhere in the body, potentially acting on blood vessels and reducing the flow of oxygen. Researchers say it is still unclear whether Covid patients’ brains will fully recover.