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Despite apparent remission from the acute phase of COVID-19, cognitive deficits are frequently reported by patients. The latter in particular evoke a feeling of mental slowness, fog and sometimes a lack of intellectual clarity – a sort of chronic phase of the disease commonly called “long COVID”. A new study, the largest of its kind in the United Kingdom, looked at the immediate and long-term impacts of SARS-CoV-2 on the brain. According to scientists, 12 to 18 months after hospitalization, some patients show serious cognitive decline, comparable to that observed after 20 years of aging.
Although previous studies have linked COVID-19 to persistent cognitive impairment, the specific mechanisms by which SARS-CoV-2 affects the brain remain unclear. This is why in this new large-scale study carried out as part of the COVID-CNS Consortium, researchers from the Universities of Liverpool, King’s College London and Cambridge have directed their research towards the analysis of biological causes and mechanisms. responsible for post-COVID cognitive deficits.
Lead author of the study, Dr Greta Wood from the University of Liverpool, said in a statement: “ After hospitalization, many COVID-19 patients report persistent symptoms, often referred to as ‘brain fog’ “. She adds: “ However, it is not yet clearly established whether these symptoms correspond to objective cognitive deficiencies, whether there is biological evidence of brain damage, and especially whether patients recover over time. ».
To carry out their research, the scientists analyzed data from 351 volunteers aged 16 and over who participated in the COVID-Central Nervous System (CNS) study of the COVID-19 BioResource program of the National Institute of Health Research (NIHR ). In this study, participants (84% of whom had received two doses of vaccine) were evaluated over a period of 384 days. Assessments included cognitive tests, blood samples to detect markers of brain damage, and magnetic resonance imaging (MRI) scans. Of the participants, 29% had severe symptoms, and on post-acute assessments, 54% of patients showed neurological complications.
Cognitive decline equivalent to 20 years of brain aging
Dr. Wood and colleagues then analyzed data from these 351 patients (with COVID-19 and without a neurological diagnosis, with or without complications). The study also included a control group of 2,927 people matched on age, gender and education level. Among hospitalized patients, some developed new acute neurological complications while others did not suffer from them. However, in both cases, the decline in the patients’ cognitive abilities proved more concerning than expected.
Wood said: “ We found that affected people, whether or not they had acute neurological complications due to Covid-19, had more severe cognitive impairment than would be expected given their age, gender and of their level of education, based on 3,000 control subjects “. Most concerning, according to the team, is that post-Covid cognitive decline in hospitalized patients is approximately equivalent to two decades of brain aging.
In the study paper published in Nature Medicinethe researchers also point out that brain images of hospitalized patients show a reduction in brain volume and lesions in specific areas. Abnormally high levels of proteins linked to brain damage were also noted. They say the link between brain damage visible in MRI scans and markers in blood tests provide concrete evidence that COVID-19 can have significant impacts on brain health, even long after initial infection.
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Professor Benedict Michael, corresponding author of the study and professor of neuroscience at the University of Liverpool, said: “ Covid-19 is not just a lung disease. Often the most seriously affected patients are those with brain complications “. He adds: “ These persistent cognitive deficits were present in people hospitalized with and without clinical neurological complications, indicating that COVID-19 alone can cause cognitive impairment without a neurological diagnosis having been made. ».
According to Michael, the next step will be to study the similarity of the chronic mechanisms identified in COVID-19 to those of other infections, including influenza. “ Our work can help guide the development of similar studies in people with long Covid, who often have much milder respiratory symptoms and also report cognitive symptoms such as ‘brain fog’, and to develop therapeutic strategies », concludes Gerome Breen, co-author of the study and psychiatric geneticist at King’s College London.
Source : Nature Medicine
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