Research suggests that long-term COVID-19 leaves unique signs in the blood that could be targeted with treatments.

Results from the UK’s largest study of coronavirus hospital admissions show long-term Coronavirus Resulting in ongoing inflammation that can be detected in the blood.

An analysis of more than 650 patients hospitalized with severe COVID-19 found that those with longer-lasting symptoms showed evidence of activation of their immune systems.

How activation occurs depends on the type of their primary symptom, such as fatigue or brain fog.

The study, led by Imperial College London, suggests that existing drugs that modulate the body’s immune system may help treat long-term COVID-19 and should be investigated in future studies.

Professor Peter Openshaw from the National Heart and Lung Institute at Imperial College London said: “One in 10 Sars-CoV-2 infections will lead to long-term infection with the new coronavirus, and an estimated 65 million people worldwide suffer from persistent symptoms. We urgently need more research to Understand this condition.”

He said the study “is an important step forward and provides important insights into what causes long COVID”.

He added: “I do think it’s a hopeful message that post-COVID, these biological pathways are activated by different forms of persistent symptoms that people didn’t imagine.

“This is what really happened to them.”

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The study, published in the journal Nature Immunology, compared 426 people with long-term COVID-19 symptoms (who had been hospitalized with COVID-19 at least six months before the study) with 233 people who had been hospitalized with COVID-19. 19 but has fully recovered.

Plasma samples were collected and levels of proteins known to be involved in inflammation and immune system regulation were measured.

Researchers found that compared with patients who fully recovered, patients with long-term COVID-19 infection showed a pattern of immune system activation that indicated inflammation of bone marrow cells — the cells that form in the bone marrow and produce white blood cells in response to injury and infection. — and the immune system activates a family of immune system proteins called the complement system.

Dr Felicity Liew, from the National Heart and Lung Institute at Imperial, said: “Our findings suggest that complement activation and bone marrow inflammation may be a common feature of long-term COVID-19 after hospitalization, regardless of symptom type.

“It is unusual to find evidence of sustained complement activation months after acute infection has resolved, suggesting that long-term COVID-19 symptoms are the result of active inflammation.

“However, we cannot be certain whether this applies to all types of long-term COVID-19, particularly where symptoms develop after non-hospital infection.”