Last week, a five-year-old boy in New York died from Covid-19-related complications. Dozens of other children are becoming sick with a similar cluster of symptoms that mirror a rare condition called Kawasaki disease. The accepted wisdom had been that children could transmit the virus, but not get sick from it. The new illness is throwing that assumption into question. Jason Gale talked to the world’s leading expert on Kawasaki disease to help unpack what is going on.