Children who get COVID-19 more than once are at higher risk of developing long COVID, new research from the University of Pennsylvania suggests. Specifically, the study published Tuesday in The Lancet Infectious Diseases found that children who get COVID twice are two times more likely to develop long COVID compared to children who only get COVID once. But generally, long COVID is associated with health complications that last more than three months after a COVID infection. The researchers found that among patients under 21 who had COVID once, there were 904 cases of long COVID per million people. The study was part of the federal RECOVER initiative designed to better understand the effects of long COVID.