Markers of brain injury developed due to COVID-19 were found in patients even months after the infection and despite blood tests measuring inflammation returning normal results, according to a new research.

Researchers from universities in the UK explained that during the acute phase of the viral infection, when symptoms develop quickly, key inflammatory proteins and brain injury markers are produced.

They analysed over 800 hospitalised patients' samples from across England and Wales.

Surprisingly, even months after being discharged from the hospital, there is on-going robust biomarker evidence of brain injury developed due to COVID-19, the researchers said in their study published in a journal, Nature Communications.

The biomarker evidence was more prominently seen in patients experiencing neurological dysfunction during the acute illness, and continued in the recovery phase in patients suffering acute neurological complications, the researchers said.

"While some neurological 'symptoms' were often mild (headache and muscle aches [myalgia]), it became clear that more significant and potentially life-changing new neurological 'complications' were occurring, including encephalitis (brain inflammation), seizures, and stroke," said Benedict Michael, Principal Investigator and Director of the Infection Neuroscience Laboratory, University of Liverpool.

The inflammatory markers, associated with abnormal immune responses in the acute phase of the disease, suggest the possibility of ongoing inflammation and brain injury that may not be detected by blood tests measuring inflammation, the researchers said.

They suggested that these biomarkers could represent therapy targets for COVID-19 and other infections causing acute brain dysfunction.

"Our study shows that markers of brain injury are present in the blood months after COVID-19, and particularly in those who have had a COVID-19-induced brain complication (e.g. inflammation, or stroke), despite resolution of the inflammatory response in the blood.

"This suggests the possibility of ongoing inflammation and injury inside the brain itself which may not be detected by blood tests for inflammation," said Michael.

Michael's team is now working to understand what the findings means for cognitive function, independence and recovery in those affected.

The research team also said that their work helps set the stage for discerning possible underlying mechanisms of these neurological complications.

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