Catching Covid makes people less intelligent, with severe infections reducing IQ the most, a study suggests.

Britons who avoided the disease typically performed best in intelligence tests, while those who ended up in hospital scored worst.

But even those who suffered only mild disease are likely to have had their cognitive abilities decline, it is believed.

Scientists from Imperial College London analysed data on more than 112,000 volunteers who took Covid tests during the pandemic.

Analysis revealed that those who were admitted to intensive care with Covid scored around nine IQ points lower on average in exams than those who avoided infection.

Britons who avoided the disease typically performed best in intelligence tests, while those who ended up in hospital scored worst. (Stock Image.)

Those who reported having long Covid – persistent symptoms such as ‘brain fog’ – scored six points lower and those with only mild infection two points lower.

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 account for other factors. 

Further examination found long-lasting cognitive impacts, even in people infected a year or more earlier.

The original Covid strain was associated with a bigger 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 on Imperial College’s React study. Dr Taquet said the results should be interpreted with caution as the study did not compare the same person before and after infection.

Those who reported having long Covid – persistent symptoms such as ‘brain fog’ – scored six points lower and those with only mild infection two points lower. (Stock Image.)

Professor Benedict Michael, director of the University of Liverpool’s infection neuroscience laboratory, said there is ‘clearly a very severely affected group’. 

But he added: ‘I haven’t yet seen convincing evidence that the vast majority of the population have been knocked back by X number of IQ points.’

Separate studies analysing brain scans taken before and after the pandemic suggest Covid infection can have an impact, even in those who had not been hospitalised.

Professor Michael said it did not appear to be the virus that was infecting the brain but a secondary consequence of infection elsewhere in the body – potentially acting on blood vessels, reducing oxygen flow. Researchers say it remains unclear if brains of Covid patients will fully recover.