Do Vaccines Really Cause Autism?

Q: What’s behind the idea that vaccines are to blame for autism?
A: There are many theories—and there’s not much scientific support for any of them. One blames the MMR (measles, mumps, and rubella) vaccine, suggesting that the measles proteins in the shot can damage a child’s stomach; a leaky gut could allow protein fragments produced during diges­tion to travel to the brain and wreak havoc. Another theory implicates the vaccine preservative thimerosal, which con­tains a form of mercury known as ethylmercury. Some believe the heavy metal causes neurodevelopmental abnor­malities that lead to autism, in part, because methylmercury (a similar compound commonly found in some fish) can damage the brain.

However, more than 10 studies comparing hundreds of thousands of children who did or didn’t receive MMR vac­cines consistently showed no increased risk of autism. And six studies comparing children who received thimerosal-based vaccines versus thimerosal-free vaccines also showed no increased risk. That said, some experts don’t think the studies were rigorous or sensitive enough to pick up an effect in a fraction of susceptible children. “If 1 in 1,000 of the kids with autism had been affected by vaccines, you would not detect it in those studies,” says Isaac Pessah, PhD, director of the Center for Children’s Environmental Health at the University of California, Davis.

That means the debate is likely to go on. Pessah believes that many questions need to be answered, such as when to vaccinate and how many shots to give a child at once. “While we’ve increased the number of vaccines that are required, we haven’t kept up the research on what is too many within a certain period of time,” he explains.

Q: Are some children more susceptible to autism after they’ve been vaccinated?
A: Most experts believe that autism has a strong genetic component, and a kid with a genetic predisposition may be susceptible to any number of insults, or “hits,” to his or her system—from vaccines, infections, or other environmental factors yet to be proven. But Pessah says it’s doubtful that vaccines alone could be the sole contributor to autism.

Next: Vaccines on trial