That's varicella, a mild version of smallpox, which no one need's to be vaccinated against any more because it has been irradiated by (drum roll) a vaccine
BY LETTING UNVACCINATED CHILDREN RUN AROUND IN A CASTLE COVERED WITH PIXIE DUST, DISNEYLAND IS REBOOTING MORE CLASSIC DISEASES THAN STAR WARS. BUT THAT'S NONE OF MY BUSINESS.