Joel Tang, M.D., an internist at the University of Utah, says he hasn’t seen data suggesting vaccines are the main cause of autism.

“This issue appears to be more of a spectrum,” he says, adding that there seems to be a connection between vaccines and other disorders. “There are a lot of diseases associated with vaccines and autism. Whether one causes the other, I don’t know. Maybe one is part of the problem and the other part of the problem is an environmental factor, but it’s certainly not completely clear.”

Duke University Health System pediatrician Dr. Jennifer Shimer agrees that not enough is known to determine causality. “There’s a huge variety of risk factors. Some are risk factors for both autism and attention deficit hyperactivity disorder. If you ask an unvaccinated parent, she’ll tell you she’s worried about vaccines, but she doesn’t know why she’s worried. My suggestion is that there are as many things to worry about as there are kids with autism. It’s something every parent is going through. So if you’ve got an allergy, you’re going to think about it because your children have allergies. What I would say is you don’t need to panic.”

But Dr. William P. Kelly, director of the Center for Vaccine Evaluation and Research at Columbia University Medical Center, concurs, saying “there has not been a good scientific study of whether it’s a true cause of autism or just a marker for things that happen at a younger age.” In addition, he says, there is no evidence that vaccines contribute to autism.

This post has been updated.

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