Scientists say Covid-19 could have a negative effect on the intelligence of people admitted to hospital with the virus, according to a new study.

Researchers found that people who had been hospitalised with Covid were more likely to get a lower score on the Great British Intelligence Test.

The drop-off was even greater among those who had recovered from the virus after being put on a ventilator, according to the study, , that analysed the results of 81,337 people who took the test between January and December 2020.

The research found that people who had been infected with the virus underperformed the most on tasks where planning, reasoning and problem-solving skills were needed when compared with those who had not had Covid and after the results had been controlled for factors such as age, gender, income and ethnic group.

The study observed that the results are consistent with reports of long Covid, where symptoms include "brain fog" and finding it hard to concentrate, Sky News reports.

The deficit recorded for people who had been put on a ventilator was the equivalent of a seven-point drop in IQ and was larger than that of people who had previously suffered a stroke and those who reported learning disabilities.

The deficits could be attributed to the ongoing symptoms of Covid-19 infection, including high temperature or breathing difficulties. Some 4.8% of participants who were ill reported having residual symptoms, including 84.1% of those who had been on a ventilator.

And the scientists who took part in the study, from Imperial College London, Kings College and the Universities of Cambridge, Southampton and Chicago, warned against drawing conclusions without brain imaging data. They did, however, say more research should be conducted.

The ability to draw firm conclusions about cause and effect is restricted by the fact that just 275 participants completed the intelligence test both before and after they were infected with the virus.

The study said: "Our analyses provide converging evidence to support the hypothesis that Covid-19 infection is associated with cognitive deficits that persist into the recovery phase."

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