Aug 27, 2001: Is there any association between the mercury in vaccines and autism?

There is a movement to attribute autism to the mercury (thimersol) in vaccines.  Dr. Brent, past president of the American Academy of Clinical Toxicology has made a few remarks regarding that association.  I thought you would find them of interest.

The people at the Autism Research Institute have been trying to promote an association between the ethyl mercury (thimerosal or mercurochrome) preservative in vaccines and autism.  They point out the diverse  manifestations of organic mercury poisoning and the diverse CNS manifestations of autism and say that  they therefore must be the same disease.  They also bolster their theory by pointing out that since thimerosal has been used in vaccines (1930s on) there has been an increase in the number of cases of autism.  They disregard both the changes in the diagnostic practices in that same period and the lack of epidemiologic support for the association.  What epidemiology does exist fails to support the association between thimerosal exposure and autism.

A certain amount of fuel was added to the fire when the FDA Modernization Act of 1997 tasked the FDA with reviewing the risk of mercury in foods and medications. This kind of activity is very common now for the FDA because many medications, medical devices and food additives that have been used for a long time have been grandfathered into use without  going through the kinds of rigorous scientific review that would be needed if they were submitted for approval today.  When they looked at this issue they found that if an infant gets the full CDC recommended schedule of vaccines

plus influenza vaccine (which would be given to special populations only) that they may get as much as 187.5 ug mercury in the first six months of life.  This amount of mercury, in the form of ethyl mercury, has never been associated with mercury toxicity or any adverse effect except an occasional hypersensitivity reaction.  The wrinkle, however, is that this exceeds the EPA Reference Dose for methyl mercury, which is 0.1 ug/kg/d.  An 'allowable" amount of mercury from methyl mercury, based on this guideline, would be 89 ug for an infant at 50th percentile of body weight for the first six months of life.  This has created a lot of unnecessary  controversy since 1) the RFD is for methyl mercury (not ethyl mercury) and 2) an RFD is a suggested average for a lifetime exposure, it has no implications for short term exceedences, which this is.  The RFD also has all of the typical EPA uncertainty factors built in so it is a very conservative number.  By the end of the first or second year vaccinated children will be under the RFD from birth on, unless they are exposed to excessive amounts of methyl mercury from other sources.

Based on the above, and some unfortunate over reactions by the American Academy of Pediatrics, the American Academy of Family Physicians, the American College of Physicians, and the Public Health Service, Thimerosal was removed from vaccines.  A major question is - are the alternatives any better?  No preservative is necessary in single dose vials.  The Thimerosal was used primarily in multiple dose vials.  Under some circumstance the price difference between the two could mean a decrease in the number of children being vaccinated.  All of this despite the fact that there has never been even the suggestion of possible mercury poisoning from Thimerosal in vaccines, except for fringe groups such as the Autism Research Institute.  Although it is possible to debate about the wisdom, or non-wisdom, of taking the Thimerosal out of vaccines, the point is mute, since it has been removed.  What is important for clinical toxicologists, however, is that this is a classic example of the misapplication of an EPA reference dose and how this can result in the emergence of groups like the ARI and the anti-vaccine lobby in general.