Some parents fear vaccinations because of Internet and media stories linking them to autism. Samuel L. Katz, MD, co-creator of the measles vaccine and chairman emeritus of pediatrics at Duke, answered a few questions about the truth behind the rumors.

How did vaccinations become linked with autism?

Autism began being linked with vaccines because of a single, flawed study in the United Kingdom in the late 1990s involving 11 or 12 children. The conclusion of this research has been proven totally false.

Sam Katz, MD

Are there scientific studies that link vaccines to autism?

No. Scientific investigations have failed to demonstrate vaccines as a cause of autism.

Are any vaccines singled out?

In the United Kingdom, the measles, mumps, and rubella (MMR) vaccine is implicated by parents as a cause of autism, in part because of the temporal relationship of the two.

That is, the first MMR vaccine is administered around 12 to 15 months of age, a typical age for the diagnosis of autism -- although there is no evidence to suggest any other connection. In this country, that theory was quickly dropped, and what persists is the idea that vaccines containing the preservative thimerosal cause autism. However, thimerosal was removed from vaccines for children (except some influenza and virus vaccines) in 2001, and the cases of autism continue to increase instead of decrease.

What causes autism?

We don’t yet know the cause of autism. I think we will find there is not a single cause, but a number of contributing factors, including genetic predisposition.

Why has the number of diagnoses of autism increased?

The definition of autism in recent years has broadened to include a whole host of learning disabilities and psychiatric disorders that, in the past, were not labeled autism.

Why do the misconceptions about autism persist?

There is an abundance of misleading and scientifically unreliable information on the Web and in the media from alleged authorities and even celebrities. However, the world’s leading health organizations -- the Academies of Pediatrics and General Practice, the Centers for Disease Control, the Institute of Medicine, and the World Health Organization -- have all agreed that vaccines do not cause autism.

What are the risks when parents refuse vaccinations?

There have been outbreaks of preventable diseases among unvaccinated children in this country -- very recently in San Diego and Hawaii. All of the cases of measles we’ve had in this country in the past 16 years have been due to importations from countries abroad where measles still exists. The disease then spread into clusters of unvaccinated children. Diseases are just a jet plane ride away, and children who are not vaccinated are at risk.