People with severe Covid-19 infections sustained cognitive impairment equivalent to losing 10 IQ points, similar to the loss incurred between 50 and 70 years of age.

Universities of Cambridge and Imperial College London scientists found people with acute Covid-19 showed signs of cognitive and mental health difficulties, including fatigue, ‘brain fog’, poor word recollection, sleep disturbances, anxiety and post-traumatic stress disorder (PTSD) six months after infection and that recovery was slow.

The findings, published in the journal of eClinicalMedicine, indicate that acute illness severity is a good indication of resulting cognitive difficulties.

Long Covid has been found to affect one in seven individuals, with symptoms being reported twelve weeks after a positive Covid-19 test. Between a third and three-quarters of patients hospitalised due to Covid-19 report suffering cognitive impairment three to six months later. These difficulties are thought to arise from inadequate oxygen or blood supply to the brain, clotting and microscopic bleeds, and damage caused by the body’s immune system.

Using the  NIHR COVID-19 BioResource, the researchers analysed data from 46 individuals who had been hospitalised between March and July 2020 at Addenbrooke’s Hospital in Cambridge with an acute Covid-19 infection. Sixteen of the patients had been put on mechanical ventilation.

Six months after having the infection, participants performed a series of tests to measure different aspects of memory, attention and reasoning. Anxiety, depression and PTSD were also assessed and the results were compared with control subjects.

Professor David Menon from the University of Cambridge said: ‘Cognitive impairment is common to a wide range of neurological disorders, including dementia, and even routine ageing, but the patterns we saw – the cognitive 'fingerprint' of COVID-19 – was distinct from all of these.’

The study found people infected with Covid-19 were less accurate and had slower response times when compared with the control population after six months. The effects were most noticeable for those who required mechanical ventilation, with survivors showing slower processing speeds and scoring poorly on tasks such as verbal analogical reasoning, which is linked with word recall.

Professor Menon added: ‘We followed some patients up as late as ten months after their acute infection, so were able to see a very slow improvement. But it is very possible that some of these individuals will never fully recover.’

The next step for the researchers is to identify biomarkers linked with Covid-19 infection which relate to neurological impairments.

Professor Adam Hampshire, lead author of the study from Imperial College London, said: ‘Around 40,000 people have been through intensive care with Covid-19 in England alone and many more will have been very sick, but not admitted to hospital. This means there is a large number of people out there still experiencing problems with cognition many months later. We urgently need to look at what can be done to help these people.’

This comes after a rapid evidence review in February concluded that vaccination against Covid-19 also protects against long Covid.