Researchers learn horrifying truth behind long Covid's main symptom - and it could affect millions of Britons

Almost two million people in the UK are estimated to be living with long Covid, a term that's used to describe the symptoms that linger long after the virus has left the body.

Patients have reported experiencing cognitive decline, or brain fog, as a result of this phenomenon. This has typically manifested in the form of memory loss or sluggish thinking.

Now, researchers from Trinity College Dublin and FutureNeuro, have found disruption to the integrity of the blood vessels in the brains of people suffering from long Covid and brain fog.

According to the researchers, people with long Covid and brain fog have these leaky vessels, but those who have long Covid without this symptom do not.

They suggest their discovery is important for the understanding of brain fog and cognitive decline – seen in some people with the condition.

It is hoped the findings, which are published in Nature Neuroscience, will help with the development of treatments in the future.

Matthew Campbell, professor in genetics and head of genetics at Trinity, and principal investigator at FutureNeuro, said: “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.

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

Colin Doherty, professor of neurology and head of the school of medicine at Trinity, and principal investigator at FutureNeuro, said: “The findings will now likely change the landscape of how we understand and treat post-viral neurological conditions.

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

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It follows a previous study which found low serotonin levels might play a role in the development of long Covid.

Researchers merged previously published datasets on the biochemical profile of several cohorts of long Covid patients who had experienced symptoms for three to 22 months after confirmed infection with the virus.

They placed these patients into eight different groups based on their clusters of symptoms. For each of these groups, they investigated the biochemical profile of 58 patients considered representative of these symptom clusters, and compared them to the biochemical profile of people while infected with Covid, as well as with the biochemical profile of people who had recovered from the virus with no remaining symptoms.

The researchers discovered that a subset of patients with long Covid had traces of the virus in their stool samples even months after infection, meaning it had remained in the gut.

While serotonin was reduced during the active SARS-CoV-2 infection, serotonin levels during infection did not predict a person’s risk of developing long Covid. However, the researchers discovered a correlation between the number of symptoms of long Covid participants had and lower serotonin levels four months later.