You know, I tackle the antivax garbage here on occasion, and while of course it's not my field of expertise, I know enough and have done enough research to understand the issue fairly well.
But Orac is the Man. When he gets the wind up about vaccinations and autism, all I can do is stand back and watch him work.
Another slice of awesomeness is Steve Novella (from Skeptics' Guide to the Universe), a practicing MD and blogger of some repute. He is more, well, medicinal when he writes about vaccination, but his writing is no less damning of antivax nonsense.
Those two should always be the first places you go when you hear some health threat like Jenny McCarthy or David Kirby make ridiculous antiscience claims. You'll get the facts from Steve and Orac, and be better armed to take on the people who want to sentence our children to diseases that might kill them.