“There’s nothing about enteroviruses that makes them love even years—they don’t have a lucky number,” says Kevin Messacar, an associate professor of pediatrics at the University of Colorado and Children's Hospital Colorado who was a coauthor on that March analysis. “The model for this whole family of viruses, which is well-described, would not predict that we would wait until 2022 for an outbreak because we missed a cycle. It would say we are continually growing the pool of susceptibles who haven’t seen that virus.”