Trinity College Study Reveals Blood Vessel Leakage as Key Factor in Long COVID-Induced Mental Fog

Mental Fog and Long COVID

A team of researchers at Trinity College Dublin has just discovered the underlying and likely cause of the “mental fog” associated with long COVID. This frequent symptom, which adds to the cognitive disorders also common in these prolonged forms of COVID, could be the consequence of blood vessel leaks in the brains of these patients. These findings, presented in the journal Nature Neuroscience, pave the way for further investigations examining the molecular events leading to post-viral fatigue and mental fog.

Brain Fog.

Brain Fog.

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Implications and Prevalence of Long COVID

This is an important discovery that brings new understanding to the mental fog and cognitive decline observed in this group of patients. It also suggests that the neurological symptoms of post-COVID syndrome could be assessed from real, observable, and measurable metabolic and vascular changes in the brain. It is estimated that 10 to 15% of those who developed symptomatic COVID will suffer from this syndrome in a lasting manner.

To date, Long COVID has up to 200 reported symptoms, among which the most frequent are fatigue, difficulty breathing, memory disorders, and other higher cognitive functions, as well as joint/muscle pain. Although the vast majority of people who had COVID recovered completely, in the minority that developed The Long type, symptoms can persist for more than 12 weeks and up to 2 years after the acute infection. Finally, among these patients suffering from long COVID, approximately 50% report neurological effects, including mental fog. Long COVID has become a significant public health problem The study correlates for the first time these neurological symptoms with:

  • A disturbance in the integrity of blood vessels in the brain.
  • This “leakage” of blood vessels (blood–brain barrier disruption) also allows for the objective distinction/detection of patients suffering from mental fog or related neurological symptoms.
  • These leaks are associated with an overactive immune system, and these two characteristics could be the main factors of the mental fog associated with Long COVID.
  • These observations also allowed the development of a form of magnetic resonance imaging particularly adapted for monitoring the brain’s microvessels.

“These observations are of ‘crucial importance’ as they specify an observable and treatable cause with the help of targeted therapies,” points out Dr. Matthew Campbell, professor of genetics at Trinity. Furthermore, the research establishes the foundations and technology necessary to better understand other neurological conditions like multiple sclerosis (MS) for which viral infection is also suspected as a trigger of pathogenesis. Proving this direct link has always been a challenge.

Read Also: Shifting Symptoms: Evolving COVID-19 Variants No Longer Impact Taste and Smell, But Fatalities Persist

Finally, the team contemplates conducting further studies on the molecular events that lead to post-viral fatigue and mental fog. In fact, similar mechanisms could be triggered by other viral infections and lead to other types of neurological dysfunction.

Final thoughts

This study’s findings, while focused on long COVID, potentially revolutionize our understanding of cognitive impairments following other viral infections. The discovery that blood vessel leakage in the brain contributes to mental fog suggests a common underlying mechanism in various post-viral syndromes. This insight could lead to more effective treatments for a range of conditions. The advancement in brain imaging techniques also marks a significant step forward in diagnosing and managing neurological disorders linked to viral infections.


Greene, C., Connolly, R., Brennan, D. et al. Blood–brain barrier disruption and sustained systemic inflammation in individuals with long COVID-associated cognitive impairment. Nat Neurosci (2024).



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