Biological ‘Fingerprints’ Of Long COVID In Blood Could Lead
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The team has received funding from the National Institute for Health Research to develop a test that could complement existing antibody tests. They also aim to use similar biological signatures to develop a test and monitor for long COVID. While most people recover from COVID-19 in a matter of days or weeks, around one in ten people go on to develop symptoms that can last for several months.

Diagnosing long COVID can be a challenge, however. A patient with asymptomatic or mild disease may not have taken a PCR test at the time of infection and so has never had a confirmed diagnosis. Even antibody tests are estimated to miss around 30% of cases, particularly among those who have had only mild disease and or beyond six months post-initial illness.

During the pilot, the team recruited 85 patients to the Cambridge NIHR COVID BioResource, which collects blood samples from patients when they are first diagnosed and then at follow-up intervals over several months. They now hope to expand their cohort to 500 patients, recruited from Cambridgeshire and Peterborough.

In their initial findings, the team identified a biomarker – a biological fingerprint – in the blood of patients who had previously had COVID-19. This biomarker is a molecule known as a cytokine produced by T cells in response to infection. As with antibodies, this biomarker persists in the blood for a long time after infection.

By following patients for up to 18 months post-infection, the team hopes to address several questions, including whether immunity wanes over time. This will be an important part of helping understand whether people who have been vaccinated will need to receive boosters to keep them protected.

As part of their pilot study, the team also identified a particular biomarker found in patients with long COVID. Their work suggests these patients produce a second type of cytokine, which persists in patients with long COVID compared to those that recover quickly and might be one of the drivers behind the many symptoms that patients experience. This might therefore prove to be useful for diagnosing long COVID.

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