Reporting evidence in an accurate way – the effects of COVID-19 on the brain

Written by Marco Bonfanti, PhD researcher at University of Strathclyde and Dr Margaret Rose Cunningham, Senior Lecturer at University of Strathclyde

Over the past two years the world has witnessed the historical event of the coronavirus disease (COVID-19) pandemic. We have got to know the severe acute respiratory syndrome coronavirus 2 (SARS-CoV 2), first reported in December 2019. The major symptoms are fever, cough, headache, fatigue breathing difficulties, loss of smell and taste, although a third of people infected do not develop any symptoms. The virus spreads when people breath in contaminated air, as the virus is found in small droplets aerosols. After being inhaled, SARS-CoV 2 infects the body through the respiratory tract. The transmission is mostly dependent on a viral spike protein, which interacts with a receptor found in lung cells.

The virus not only affects the respiratory system, but over time more research has highlighted side effects in other areas of the body, such as the cardiovascular system, the gastrointestinal tract, and the nervous system. The action of the virus in the latter context is clear when looking at symptoms. Loss of taste and smell are very common and often arise before the respiratory problems. Since the outbreak of the pandemic, extensive research investigated how the virus can damage the brain. There are two main theories, one where the effect occurs directly from the infection, and another where the virus stimulates the immune system to cause inflammation in the brain. Inflammation is the body response to harmful stimuli, which results in heat, pain, redness, swelling and loss of function.

The UK Biobank is a biomedical database, containing health information from half a million UK participants. In a recent study, Dr Douaud and colleagues at the University of Oxford, used the data to compare brain scans of patients before and after contracting COVID-19. This study was the largest investigation on the effects of COVID on the human brain to date, as it included 785 patients (401 infected – 384 controls). A limitation of this study was however the restricted age range of the participants pool, which was between 51 and 81 years old. Moreover, using a UK database led to the ethnicity of the participants being almost entirely white people. The paper reports that even in mild cases of covid, infected patients took a longer time to complete numeric and alphanumeric cognitive tasks. When looking at what regions of the brain were impacted by the infection, brain scans revealed a modest loss of grey matter thickness in regions mainly associated with smell. 

This study was commented on in an article in The Guardian by the scientist Eric Topol, an expert that stood for evidence-based solutions to treat COVID-19. During the past years we have witnessed how easy it is to report COVID-19 studies in a sensationalistic way, often causing fear in the reader. In this case, the opinion piece reported the key findings in a fair and accurate manner in line with the evidence available from the published study. It was emphasised that this was the largest COVID brain imaging study to date, and how COVID-19 infection might cause grey matter loss and cognitive decline. The limitations of the study were also highlighted. A major one was that brain scans were taken before the outbreak of the widespread omicron variant, which may affect the brain differently than the initial viruses.

Should we then be worried about our brain function if we are infected by COVID-19? The answer is not really. Despite being the largest study to date, 400 patients are still not a representative sample of the global scale of COVID-19, especially considering a cohort of patients of the same ethnicity. Moreover, loss of grey matter and cognitive decline are a physiological event that happen anyway as we age. The greatest risk is therefore in the old population, who may have their smelling impaired after being infected with the virus.