https://www.nbcnews.com/health/health-news/long-covid-cause-study-immune-system-complement-response-rcna134530

Scientists have identified a persistent change in a handful of blood proteins in people with long Covid that indicates that an important part of their immune system remains on high alert for months after an acute infection.

The findings, published Thursday in the journal Science, could help explain what causes the persistent fatigue, brain fog and other debilitating symptoms of long Covid, as well as pave the way for diagnostic tests and potentially, a long-awaited treatment, experts say. 

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