Scientists at Trinity College Dublin have discovered the underlying cause of “brain fog” linked to long COVID.

Tens of thousands of people across Ireland say they are experiencing symptoms of long COVID – including fatigue, shortness of breath, problems with memory and muscle pain.

An Ireland Thinks poll carried out in September 2023 found that more than 5% of respondents are actively living with self-reported symptoms of long COVID – suggesting more than 192,000 people across the country could be impacted.

One of the main symptoms reported by patients is brain fog – and Trinity scientists now believe they understand what causes it.

It is hoped the study can lead to new treatments, not only for long COVID but for other neuro-degenerative illnesses like multiple sclerosis (MS).

'Leaky' blood vessels

Published in Nature Neuroscience today, the Trinity team discovered “disruption to the integrity of the blood vessels” in brains of patients with long COVID and brain fog.

The blood vessel “leakiness” was not found in people with long COVID but no brain fog. 

The team, led by scientists at the Smurfit Institute of Genetics in Trinity, also found a new method of brain scanning to show how “long COVID can affect the human brain’s delicate network of blood vessels”. 

'Crucially important'

Head of Genetics at Trinity Professor Matthew Campbell said this discovery is “critically important”. 

“Understanding the underlying cause of these conditions will allow us to develop targeted therapies for patients in the future,” he said. 

“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.” 

MRI scans in patients with Long-COVID with or without “brain fog". Image: Trinity College Dublin

Head of Medicine Professor Colin Doherty also noted that the study, conducted “at a time of national crisis”, is a “testament to the skill” of the team. 

“The findings will now likely change the landscape of how we understand and treat post-viral neurological conditions,” he said. 

“It also confirms that the neurological symptoms of long COVID are measurable with real and demonstrable metabolic and vascular changes in the brain.” 

Long COVID

COVID cases with symptoms that last longer than 12 weeks is considered long COVID. 

Long COVID has up to 200 reported symptoms, including problems with memory and muscle pain. 

Just under 50% of them report some form of lingering neurological effect such as cognitive decline, fatigue and brain fog.