Get the Mercury Out! Is There a Link Between Childhood Vaccinations and Autism?

It’s one of the most vigorously fought battles in medicine: Does mercury in childhood vaccines cause autism?

A handful of studies have refuted the relationship, and most mainstream medical organizations have pooh-poohed it. But advocates, including the parents of many autistic children, continue to cling to their belief that mercury causes autism. Now, a new study casts even more doubt on the theoretical link between mercury in vaccines and autism.

Research published in the January 2008 Archives of General Psychiatry documents the meteoric rise in classic autism case reports included in the records of the California Department of Developmental Services, one of the largest such databases in the country. For five-year-olds, there was an approximately eight-fold rise in the rate of classic autism between those born in 1990 and those born in 2001.

But the study took its analysis one step further. It found no evidence that autism reports declined when mercury-based thimerosol – a preservative used to prevent vaccines from becoming contaminated – was removed from childhood vaccines. The rate of increase in autism reports continued unabated, even as thimerosol exposure declined dramatically.

Autism is characterized in its “classic” form by repetitive movements, reduced social interactions and communication difficulties, but the condition has been expanded of late to encompass a range of less severe conditions such as Asperger’s Syndrome. As the California data confirm, even the diagnosis of “classic” autism is on the rise.

On that much we can all agree. But when it comes to deciding what’s behind what autism advocates have termed an “epidemic,” the gloves come off. Some point to changes in disease reporting patterns or the expansion of the disease definition: as the list of symptoms for a disease grows, there are certain to be more diagnoses. (Public Citizen favors this interpretation.) Others cite infectious causes and pollutants as potential causes of the affliction.

And then there’s the vaccine hypothesis. The number of required childhood vaccinations in the U.S. has increased in the last two decades, coinciding with the period during which the autism rate has been rising astronomically. And autism symptoms are often first noted by parents shortly after an immunization. (Of course, there are so many required vaccines nowadays, it’s almost guaranteed that new symptoms will arise not too long after an injection.) So might the vaccines themselves, or chemicals in the vaccines, be responsible for the rise in autism?

In the late 1990s, the Food and Drug Administration realized that cumulative mercury exposures among children undergoing the recommended set of vaccinations might actually exceed safe levels. So, out of caution, the U.S. Public Health Service and the American Academy of Pediatrics recommended in 1999 that thimerosol be removed from childhood vaccines. By about 2002, this had largely been accomplished, except for the flu vaccine. (Thimerosol-free flu vaccine is available, but quantities are limited.)

Some saw the compound’s removal as an admission of guilt: Why would thimerosol be removed if it wasn’t dangerous?

To others, it presented the opportunity to gather some data, for surely if thimerosol was a major cause of autism, autism rates should decline (or at least not rise as fast) once the supposed cause was eliminated. But the new study found no evidence to bolster that theory.

Granted, the new data do not wholly exclude thimerosol as a cause of some cases of autism. But, even if autism turns out to have multiple causes, the data make clear that thimerosol would have to be, at most, a minor factor.

In any event, other than the flu vaccine, there is next to no thimerosol exposure in childhood vaccines anymore, so if there ever was a problem, it’s been largely solved. It is time to move on from this rather fruitless debate to finding more likely causes and more promising treatments for this devastating condition.