Another one from John Timmer at Ars:

Despite the amazing benefits, immunization rates have been falling, driven by a fear that vaccines cause health problems such as autism. The autism risk has been both thoroughly debunked and the paper that originally suggested it turned out to be the product of an unethical, financially motivated individual. Despite this debunking, surveys show that a quarter of US parents think that vaccines can trigger autism, and rates of vaccination have continued to fall in many states. A new study looks at incoming kindergartners in California, and finds that the lack of vaccination is threatening herd immunity in some schools, and that some measures of risk have doubled in just three years. […]

Herd immunity occurs when a few unvaccinated children are protected by the fact that almost everyone around is vaccinated and therefore cannot infect them. It’s important for those for whom vaccines have not worked, those who have immune problems, or those who cannot be vaccinated due to specific health risks. But it requires very high rates of vaccination, typically 80-90 percent. And, in California, it’s at risk of breaking down. “The number of kindergartners attending schools in which there were more than 20 exempted kindergartners almost doubled (from 1937 in 2008 to 3675 in 2010),” the authors note.

Full Story: Ars Technica: Widespread vaccine exemptions are messing with herd immunity