Do Vaccines Cause Autism? Health experts say parents shouldn't worry about current round of vaccines

Dear EarthTalk: Is it true that toxins in some common childhood vaccines cause autism, and if so should I not have my children vaccinated?

—Reese Falk, Brewer, ME

Researchers studying neurological disorders in children have zeroed in on thimerosal, a mercury-based preservative once common in vaccines, as a potential culprit in the rise of autism cases in recent years. Preservatives like thimerosal are used to prevent infection in the event that a dose is accidentally contaminated. Due to recent heightened concerns over the potential effects of mercury on child brain development, though, most vaccines for U.S. children under the age of six no longer contain thimerosal.

vaccines cause autism
Lab technician gets vaccines ready. Credit: Sanofi Pasteur, FlickrCC

The issue received considerable attention following a June 2005 Rolling Stone article entitled “Deadly Immunity,” by environmental lawyer and activist Robert F. Kennedy, Jr. Kennedy claims that federal officials covered up proven scientific links between thimerosal and a 15-fold increase in autism cases since 1991. At that time, the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control (CDC) had recommended that three additional vaccines containing thimerosal be given to infants.

“More than 500,000 kids currently suffer from autism, and pediatricians diagnose more than 40,000 new cases every year,” says Kennedy. “The disease was unknown until 1943, when it was identified and diagnosed among 11 children born in the months after thimerosal was first added to baby vaccines.”

Due to the concerns of Kennedy and thousands of like-minded parents, vaccine manufacturers have begun to phase thimerosal out of injections given to American infants. Unfortunately, though, they have continued to export their back stock of tainted vaccines to developing countries, according to Kennedy. For instance, autism was virtually unknown in China prior to the introduction of thimerosal by U.S. drug makers in 1999; today approximately 1.8 million Chinese children suffer from the disorder. Even so, industry groups complain that a direct link between autism and thimerosal has not been definitively proven.

To be safe, parents may want to ask their pediatrician if the vaccines he or she uses contain thimerosal. Some flu and tetanus shots containing thimerosal are still given to pre-teens in the U.S., although preservative-free versions are usually available upon request. The FDA provides a listing on its website of common children’s vaccines and their thimerosal content, if any, and also lists thimerosal-free alternatives.

Parents who are considering not vaccinating their children at all should know that this is a hotly debated topic—and this column is in no position to recommend a course of action. Most medical professionals argue that vaccines have saved more lives than any other kind of medical intervention and recommend their use to guard against such diseases as polio, diphtheria, rubella, hepatitis B and many others. On the other hand, critics believe that the medical benefits of vaccines are exaggerated and that negative reactions owed to toxic chemical ingredients in many vaccines have been grossly under-reported.

CONTACTS: CDC Mercury and Vaccines Page,; FDA “Thimerosal in Vaccines” Information,; “Deadly Immunity,”