The Centers for Disease Control and Prevention estimates that up to 23 million Americans have been affected by long COVID. That term describes a wide variety of conditions, from brain fog and chronic fatigue to neurological problems and blood clots, that persist for months or even years after infection. But clear answers about exactly how often this happens, who’s most at risk and why, are still elusive. Marketplace’s Meghan McCarty Carino speaks with Emily Pfaff of the University of North Carolina at Chapel Hill, who uses artificial intelligence to analyze electronic health records, looking for patterns that might better identify the syndrome and treat patients.