Public health scientists and clinicians tout vaccines as one of the greatest achievements of modern medicine. But for many ordinary Americans vaccines have become controversial. Young parents are concerned at the sheer number of shots -- some 26 inoculations for 14 different diseases by age six -- and follow alternative vaccination schedules advocated by gurus like Dr. Robert Sears. Other parents go further. In communities like Ashland, Oregon, up to one-third of parents are choosing not to vaccinate their kids at all. And some advocacy groups, like Generation Rescue, argue that vaccines are no longer a public health miracle but a scourge; they view vaccines as responsible for alarming rises in certain disorders, including ADHD and autism. This is the vaccine war: On one side sits scientific medicine and the public health establishment; on the other a populist coalition of parents, celebrities (like Jenny McCarthy), politicians and activists. It's a war that increasingly takes place on the Internet with both sides using the latest social media tools, including Facebook and Twitter, to win the hearts and minds of the public.