Years after the discovery of the COVID-19 virus, many people still wonder whether their current symptoms can be traced back to the illness they contracted one, two, or even years ago. Up to 65 million people worldwide have contracted long COVID1, according to one estimate, and more than 200 symptoms of long COVID have been identified—from brain fog to difficulty breathing. There is still a lot we need to learn about long COVID, but a new finding just shed light on one potential trigger.