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With 17 million adults reporting long COVID symptoms like brain fog and fatigue, the idea of viral persistence has gained traction.

"At the beginning of the pandemic, we never expected to have these discussions about SARS-CoV-2 persistence," said Michael Peluso, MD, MHS, of the University of California San Francisco. "It was just not part of our framework for coronaviruses."

Early papers identified SARS-CoV-2 antigens in blood or tissue, but many were small studies evaluating immunocompromised people, Peluso noted. "None addressed the specificity of the assay, and a common criticism was that this could all be a false-positive signal," he told MedPage Today.

But in research published last month in Lancet Infectious Diseases, Peluso and colleagues studied plasma samples from 171 immunocompetent people who had COVID, using an ultrasensitive assay to measure the concentration of SARS-CoV-2 antigens, including the S1 subunit of spike, full-length spike, and nucleocapsid. These samples were compared with 250 pre-pandemic samples from people who never had COVID.

The researchers found that a quarter of COVID-infected people had SARS-CoV-2 antigens in their blood for up to 14 months after infection. The most common was spike. Head over to MedPage Today to read more about it.