A severe coronavirus infection, involving hospitalisation and ventilator support, has a substantial impact on a recovered patient's intelligence as part of wider "Long-COVID" symptoms, a UK study has found.

Scientists tested 81,337 participants between January and December 2020 with a clinically validated web-optimised assessment as part of the Great British Intelligence Test. The questionnaire items captured self-report of suspected and confirmed COVID-19 infection and respiratory symptoms.

"These results accord with reports of long-COVID, where "brain fog'', trouble concentrating and difficulty finding the correct words are common," notes the study published in 'The Lancet - EclinicalMedicine' journal last week.

"The scale of the observed deficit was not insubstantial... When examining the entire population, the deficits were most pronounced for paradigms that tapped cognitive functions such as reasoning, problem solving, spatial planning and target detection whilst sparing tests of simpler functions such as working-memory span as well as emotional processing," it said.

One possibility was the observed cognitive deficits related to ongoing symptoms of the deadly virus, such as a high temperature or respiratory problems, with 4.8 per cent of participants who were ill reporting residual symptoms.

People who had recovered from COVID-19, including those no longer reporting symptoms, exhibited "significant" cognitive deficits versus controls when controlling for age, gender, education level, income, racial-ethnic group, pre-existing medical disorders, tiredness, depression and anxiety.

"The deficits were of substantial effect size for people who had been hospitalised, but also for non-hospitalised cases who had biological confirmation of COVID-19 infection. Analysing markers of premorbid intelligence did not support these differences being present prior to infection."

"Finer grained analysis of performance across sub-tests supported the hypothesis that COVID-19 has a multi-domain impact on human cognition," the findings conclude.

The scientists said the results accord with reports of "Long COVID" cognitive symptoms that persist into the early-chronic phase.

They say the findings should act as a "clarion call" for further research with longitudinal and neuroimaging cohorts to plot recovery trajectories and identify the biological basis of cognitive deficits in SARS-COV-2 or COVID-19 survivors.

The study entitled "Cognitive Deficits In People Who Have Recovered From COVID-19'' involved researchers from Imperial College London, King's College and the Universities of Cambridge, Southampton and Chicago.