SEVERAL YEARS AGO, infectious disease specialist Paul A. Offit suddenly found himself the target of hate mail and phone threats. After spending 25 years working on the development of the rotavirus vaccine RotaTeq, which the FDA approved in 2006 for all infants, Offit’s championing of childhood vaccines met with the fierce opposition of parents convinced that the measles-mumps-rubella (MMR) vaccine as well as the preservative thimerosal, found in all vaccines, cause autism.

In his book Autism’s False Prophets: Bad Science, Risky Medicine, and the Search for a Cure, Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, exposes the junk science of the researchers who advanced these two hypotheses. Although the vaccine link to the disorder has been widely discredited, Offit says a general fear of vaccines hasn’t abated—with disastrous effects.

Q: Why write a book certain to inflame your critics?
A: Because the misperception that vaccines cause autism has done a lot of harm by convincing parents not to vaccinate their children. And because that hypothesis has diverted resources from promising leads about autism’s cause and because children have been subjected to dangerous therapies to cleanse them of the supposedly harmful substances in vaccines.

Q: Who’s promoting the idea that MMR and thimerosal cause autism?
A: A small group of media-savvy, politically connected parents who are very, very angry because they think science hasn’t advanced fast enough to determine what causes autism and, worse, that no one is paying attention to the possibility that vaccines might be the cause. But attention was paid. There are now 18 studies showing that MMR and thimerosal don’t cause autism—research that happened very quickly in response to a hypothesis born only 10 years ago. I think most parents of children with autism are done with the vaccine hypothesis now.

Q: But the Centers for Disease Control and Prevention reported that in the first seven months of 2008, measles cases were at their highest since 1996, totaling 131.
A: Some parents are still delaying or withholding vaccines, and we’re starting to see children die from preventable diseases. There have been three cases of Hib meningitis in Minnesota, and late last year one child died. This year we’ve had at least three deaths from Hib in Philadelphia, and three cases elsewhere. These are watershed events. There is this notion among some parents that children are getting too many vaccines too soon, that it’s more than their immune systems can handle. That doesn’t make sense immunologically; vaccines are a very small part of the foreign proteins that our bodies handle every day.

Q: How many children are we talking about?
A: The percentage of children who don’t get any vaccines is very small—less than 1%. But based on my discussions with pediatricians and people at the CDC, I’m guessing that 15% of parents are delaying or withholding some vaccines.

Q: Is this a new phenomenon?
A: No. Fear of vaccines has been around since the first vaccine, which was for smallpox. The pertussis [whooping cough] vaccine was said to cause permanent brain damage; the hepatitis B vaccine, sudden infant death syndrome and multiple sclerosis; the Hib vaccine, diabetes. But science has been quick to counter those claims. The hard part has been communicating the science to the public. The media is forced to present both sides, even if only one is supported by science.

Q: So it’s inevitable that some parents will choose not to vaccinate their children?
A: For my generation and my parents’ generation, vaccines were an easy sell. I got measles, mumps and chicken pox; and my parents, when they were children, saw their classmates die of diphtheria. But young people today didn’t grow up with these diseases. The benefit of vaccines for them is an article of faith, and there has been an erosion of that faith. Now, as children who are under- or unvaccinated are hospitalized for measles or die from Hib, immunization rates will go up again. Then, in another five or 10 years, rates will erode again.

Q: Can anything be done?
A: Philosophical exemptions for immunizations should be more difficult to get in the 21 states that offer them. Before they sign, people should be required to take part in an educational program. Give us a chance to ask whether forgoing immunization is really what you want for your child.