Parents of children with autism don’t get much good news: It’s still not clear what causes the often devastating disorder, which affects as many as 1 in 150 children and for which there is no cure. As a result, theories abound on potential causes, the most notorious being the 1960s-era notion of “refrigerator mothers.”
In recent years, much energy has been expended on arguing whether vaccines could cause autism: Some parents think that the measles-mumps-rubella vaccine or thimerosal, a mercury-based preservative in other vaccines, is the culprit. Scientists, on the other hand, think autism is largely genetic, and have focused on looking for genes that could be at fault. That disconnect has been frustrating to parents and sometimes dangerous; an unproven treatment known as chelation therapy, which leaches heavy metals such as mercury from the body, resulted in the death of a 5-year-old boy in 2006 after he was administered the wrong drug.
The best evidence to date that vaccines are not responsible is published today in the Archives of General Psychiatry. Researchers with the California Department of Public Health found that the number of new cases of autism reported in California has risen consistently for children born from 1989 through 2003, which includes the period when thimerosal was phased out. Studies in other countries, including one from Canada published in 2007, have also exonerated vaccines and thimerosal.