Measles could once again become native in the U.S., disease experts worry, as an outbreak in California linked to Disneyland has put a spotlight on a growing failure to vaccinate that's helping the disease to spread. While 94 percent of California kindergarteners were fully inoculated against the virus last school year, according to the U.S. Centers for Disease Control and Prevention, there are clusters where vaccination is much lower. In some pockets of California, as much as a quarter of children are undervaccinated -- putting them at risk of both contracting the disease and becoming a nexus of future spread.
