kindergarten

Starr Roden, left, a registered nurse and immunization outreach coordinator with the Knox County Health Department, administers a vaccination to Jonathan Detweiler, 6, at the facility in Mount Vernon, Ohio.
Paul Vernon / Associated Press

States are heatedly debating whether to make it more difficult for students to avoid vaccinations for religious or philosophical reasons amid the worst measles outbreak in decades, but schoolchildren using such waivers are outnumbered in many states by those who give no excuse at all for lacking their shots.