The findings, published in the journal eClinicalMedicine, emerge from our COVID-19 BioResource, with 46 patients consenting to join the cohort after admission to Addenbrooke's Hospital - part of Cambridge University Hospitals NHS Foundation Trust - between March and July 2020 for in-hospital care, on the ward or intensive care unit. The results of the study suggest the effects are still detectable more than six months after the acute illness, and that any recovery is at best gradual.
There is growing evidence that COVID-19 can cause lasting cognitive and mental health problems, with recovered patients reporting symptoms including fatigue, ‘brain fog’, problems recalling words, sleep disturbances, anxiety and even post-traumatic stress disorder (PTSD) months after infection. In the UK, a study found that around one in seven individuals surveyed reported having symptoms that included cognitive difficulties 12 weeks after a positive COVID-19 test.
While even mild cases can lead to persistent cognitive symptoms, between a third and three-quarters of hospitalised patients report still suffering cognitive symptoms three to six months later.
The individuals underwent detailed computerised cognitive tests an average of six months after their acute illness using the Cognitron platform, which measures different aspects of mental faculties such as memory, attention and reasoning. Scales measuring anxiety, depression and post-traumatic stress disorder were also assessed. Their data were compared against matched controls.
COVID-19 survivors were less accurate and with slower response times than the matched control population – and these deficits were still detectable when the patients were following up six months later. The effects were strongest for those who required mechanical ventilation.
Survivors scored particularly poorly on tasks such as verbal analogical reasoning, a finding that supports the commonly-reported problem of difficulty finding words. They also showed slower processing speeds, which aligns with previous observations post COVID-19 of decreased brain glucose consumption within the frontoparietal network of the brain, responsible for attention, complex problem-solving and working memory, among other functions.
Professor David Menon from the Division of Anaesthesia at the University of Cambridge, the study’s senior author, 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.
“We followed some patients up as late as ten months after their acute infection, so were able to see a very slow improvement. While this was not statistically significant, it is at least heading in the right direction, but it is very possible that some of these individuals will never fully recover.”
There are several factors that could cause the cognitive deficits, say the researchers. Direct viral infection is possible, but unlikely to be a major cause; instead, it is more likely that a combination of factors contribute, including inadequate oxygen or blood supply to the brain, blockage of large or small blood vessels due to clotting, and microscopic bleeds. However, emerging evidence suggests that the most important mechanism may be damage caused by the body’s own inflammatory response and immune system.
Professor Adam Hampshire from the Department of Brain Sciences at Imperial College London, the study’s first author, 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.”
Along with support from the BioResource, the study was funded by the NIHR Cambridge Biomedical Research Centre and the Addenbrooke’s Charitable Trust, with additional support from the NIHR Cambridge Clinical Research Facility.
The COVID-19 BioResource was rapidly established in March 2020 in response to the pandemic, with healthcare workers, patients and controls recruited to the cohort to provide an extensively characterised panel of volunteers for researchers looking into both the virus itself and later the vaccine response in different populations.
Our COVID-19 BioResource has to date supported over 45 research studies and recruited more than 8,000 participants. Watch our short video outlining our response to the pandemic and hear from University of Cambridge researcher Professor Ravi Gupta and his team on the vital role of the BioResource in their work investigating the virus and vaccine responses.
Our volunteers have taken part in a wide range of studies looking at different COVID-19 outcomes and we’re proud to have supported so many leading researchers in their efforts to understand this virus.
Another related study using BioResource governance and research framework - COVID-19 Clinical Neuroscience Study (COVID-CNS) - is co-led by Professor Menon along with Professor Ed Bullmore from Cambridge’s Department of Psychiatry and teams at the University of Liverpool and King’s College London. COVID-CNS has recently recruited its 500th patient and passed the 1-year mark, with the team aiming to identify biomarkers that relate to neurological impairments as a result of COVID-19, and the neuroimaging changes that are associated with these.
Anyone can join the NIHR BioResource, whether living with a health condition or not. It is important we have diverse representation from across the country in our national panel of volunteers so that we can continue to support vital health research studies that benefit everyone.
If you are a researcher interested in using the BioResource to support your work, please visit our information page.