Researchers at Boston hospitals may have found a biomarker for long COVID

The marker, found in blood samples, could help doctors identify people with long COVID who are most likely to benefit from new treatment.

A former nurse practitioner now living with long COVID, Mallory Stanislawczyk suffers from fatigue and a racing heartbeat so severe she must use a wheelchair and receive saline infusions three times a week. She is one of many people trying to help others with long COVID symptoms recognize their condition as a disability. Matt Roth/The Washington Post

Over two years since COVID-19 first spread across the world, scientists are just scratching the surface of what is known about the lingering effects of the virus. Perhaps the most prominent aftereffect is long COVID, also known as post-acute sequelae of COVID-19 or PASC. Last month, data released by the federal government showed that nearly one in five people who once reported a positive COVID case are currently experiencing symptoms of long COVID. 

Now, researchers in Massachusetts have discovered a potential marker that could help inform the diagnosis and treatment of long COVID. 

This biomarker, found in blood samples, was identified by investigators from Brigham and Women’s Hospital and Massachusetts General Hospital. They analyzed 63 plasma samples from patients with long COVID, according to a release. 


In more than half of the patient samples they reviewed, scientists found the spike protein of SARS-CoV-2, which helps the virus spread throughout a body. This protein was found circulating in the blood of patients up to a year after they were diagnosed with an active infection, according to the release. 

This information seems to suggest that the virus persists in the body, and lingers in an “unknown viral reservoir,” researchers said. Viral reservoirs are anatomical sites where viruses accumulate and persist, according to the scientific journal Nature

They compared this finding to a previous study of children with multi-system inflammatory syndrome. During that research, a viral reservoir was found in the gastrointestinal tract of patients. From there, scientists were able to set up a clinical trial for a new treatment of the condition. 

“If PASC is the result of persistent viral replication in tissues outside the lung, it may help explain why patients experience the symptoms of long COVID,” said David Walt, Professor and Principal Investigator at the Department of Pathology at Brigham.

The samples analyzed by Walt and his colleagues were provided by MGH. 

“Identifying this biomarker in the blood gives us a handhold on this condition, gives us a potential therapeutic target, and may help us identify people with long COVID who are most likely to benefit from new treatment approaches,” he said in a statement. 


Many are now labeling the COVID-19 pandemic as a mass-disabling event, with long COVID symptoms forever changing the lives of millions of people.

Recent data from the National Center for Health Statistics shows that about 1 in 13 adults in the US have long COVID symptoms. These are defined as symptoms lasting three or more months after first contracting the virus, and ones that they didn’t have prior to their COVID-19 infection. Long COVID symptoms can include cognitive issues, difficulty breathing, chronic pain, and fatigue. 

The American Academy of Physical Medicine and Rehabilitation, which keeps a running dashboard of long COVID data, estimates that there are over 26 million cases of long COVID in the country. California has the most estimated cases, with over 3 million. The organization estimates that there are more than 521,000 long COVID cases in Massachusetts. 


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