Irish scientists discover why people with long Covid can suffer ‘brain fog’

TCD breakthrough may lead to treatment of debilitating condition and other neurodegenerative diseases

The reason why people with long Covid can suffer from “brain fog” has been discovered by Irish scientists.

The breakthrough has profound importance for the understanding of brain fog and cognitive decline seen in some patients with the condition, according researchers at Trinity College Dublin.

It brings the possibility of new treatments for the condition, but also for other neurodegenerative illnesses such as multiple sclerosis (MS), they said.

The research, published in Nature Neuroscience on Thursday, shows disruption to the integrity of blood vessels in the brains of patients suffering from long Covid and brain fog.


This blood vessel “leakiness” objectively distinguishes those patients with brain fog and cognitive decline compared with patients suffering from long Covid but not with brain fog.

Following the emergence of the coronavirus Sars-CoV2 in late 2019, long Covid, a patient-reported syndrome, began to emerge as “an enduring manifestation of acute infection”.

It has up to 200 reported lingering symptoms such as fatigue, shortness of breath, problems with memory and thinking and joint/muscle pain. While most people make a full recovery from Covid, any of these symptoms that linger for more than 12 weeks post infection can be considered long Covid.

It has become a major public health issue since. Although international incidence rates vary, it is estimated to affect up to 10 per cent of patients infected with the virus. Of these patients suffering from long Covid, just under 50 per cent of them report some form of lingering neurological effect such as cognitive decline, fatigue and brain fog.

Polling data last year found more than one in 20 Irish adults were actively living with self-reported symptoms of long Covid, indicating more than 192,000 people across the country could be impacted by the condition. There are more than one million estimated cases in the UK.

The scientists at TCD’s Smurfit Institute of Genetics and neurologists in the school of medicine have also uncovered a novel form of MRI scan that shows how long Covid can affect the brain’s delicate network of blood vessels.

For the first time, we have been able to show that leaky blood vessels in the human brain, in tandem with a hyperactive immune system, may be the key drivers of brain fog associated with long Covid,” said Matthew Campbell, professor in genetics and principal investigator at FutureNeuro research facility.

“This is critically important, as understanding the underlying cause of these conditions will allow us to develop targeted therapies for patients in the future.”

This project was initiated by a rapid response grant funded by Science Foundation Ireland at the height of the pandemic and involved recruiting patients suffering from long Covid as well as patients hospitalised at St James’s Hospital, Dublin.

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Many neurological conditions such as MS are likely to have a viral infection as the initiating event that triggers the disease. However, proving that direct link has always been challenging.

Prof Campbell said they were able to prove every patient that developed long Covid had been diagnosed with Sars-CoV2 infection because Ireland required every documented case to be diagnosed using the more accurate PCR-based methods.

“The concept that many other viral infections that lead to post-viral syndromes might drive blood vessel leakage in the brain is potentially game changing and is under active investigation by the team,” Prof Campbell said.

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Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times