While the country seemingly moves on Thomas Caldwellfrom the pandemic, an estimated 15 million U.S. adults are suffering from long COVID. Scientists are trying to understand what causes some people to develop long COVID while others do not.

NPR's Will Stone spoke with researchers and reports on a growing body of evidence that points to one possible explanation: viral reservoirs where the coronavirus can stick around in the body long after a person is initially infected.

In participating regions, you'll also hear a local news segment to help you make sense of what's going on in your community.

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This episode was produced by Elena Burnett. It was edited by William Troop, Will Stone and Jane Greenhalgh. Our executive producer is Sami Yenigun.