LARRY BRILLIANT: Autism is caused by a lot of factors that we don't fully understand, but vaccines are not one of those factors.

I live in Marin County. I live in the epicenter of the anti-vax movement. It's pretty obvious I have not been very successful in my own county in persuading people. And I understand this is a very complicated business. Measles, for example, one of the M's in MMR, measles spreads faster than any other virus we've ever seen. One case can give rise to 20 or 30 cases in two weeks. If we had a lot of measles around and there were a lot of children getting sick all the time we wouldn't be looking at the marginal question of whether vaccinating my child or not was a good idea; we'd be rushing to get the measles vaccine. And that's what happened. When polio was around, and you always knew somebody in the neighborhood who was paralyzed in an iron lung, we all rushed to get that polio vaccine. In fact, there's photographs of parents standing in line for four or five hours to get the Salk vaccine or the Sabin vaccine. When there's no polio in the United States and we're down to 18 cases of polio in Pakistan, we're this close to eradicating polio, when there's no measles around we change our calculus. Why should I subject my child to a one in a million risk if there's less than a one in a million chance of them getting the disease?

And this is where it becomes hard because we have to talk about prevention of a disease that still exists in the world but not in our neighborhood. It's not front of mind. And a lot of these parents who are against vaccines are wonderful, the most wonderful people, they're just trying to do the right thing for their kids. But vaccines are the best thing science has ever given us. It's saved hundreds of millions of children's lives. It eradicated smallpox. It has reduced the population explosion. I know that that's pretty paradoxical, but as long as there are vaccines children will not die as they did when I was in India—there were places that 50 percent of kids died before the age of five. When that happens parents have many more babies because they expect to lose so many. Vaccines have changed that.