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June 19, 2005

Thimerosal: correlation, causation, and conspiracy

This is the first of two posts about thimerosal-containing vaccines and autism. The first post is about the scientific evidence for a connection between thimerosal-containing vaccines and autism. The second post will discuss whether pharmaceutical companies and federal regulators have responded appropriately to thimerosal concerns.

Until recently, I was agnostic about the safety of thimerosal. Then Orac stepped into the fray, repeatedly. I was thus inspired to investigate further.

As far as I can tell, the thimerosal/autism connection is totally unsupported by evidence. Autism diagnoses have been rising steadily over the past few decades. However, we shouldn't infer that autism incidence must therefore be increasing. Autism awareness has also risen steadily over the years, thanks to the hard work of activists, researchers, and clinicians. The diagnostic category has also broadened significantly since the 1940's to include an entire spectrum of developmental disorders.

Thimerosal made its debut as a vaccine preservative in the 1930s. The term "autism" had been used since 1911 to describe the symptom of extreme pathological introversion. However, autism wasn't recognized as a distinctive developmental disorder until 1943.

According to the World Health Organization's statement on thimerosal, concern over the safety of thimerosal was initially sparked by a confusion. After 70 seemingly uneventful years of widespread use, thimerosal came under scrutiny from the FDA in 1999. During a review of vaccination recommendations, some experts became concerned that the cumulative mercury exposure in the standard vaccine schedule exceeded U.S. exposure limits for mercury. As it turned out, the exposure limits were for set methyl mercury, whereas thimerosal is a derivative of ethyl mercury. The FDA had been treating ethyl and methyl mercury as equivalent, but we now know that two compounds have significantly different toxicological properties:

Expert consultation and data presented to the Global Advisory Committee on Vaccine Safety (GACVS) on 20-21 June 2002 indicate that the pharmacokinetic profile of ethyl mercury is substantially different from that of methyl mercury. The half-life of ethyl mercury is short (less than one week) compared to methyl mercury (1.5 months) making exposure to ethyl mercury in blood comparatively brief. Further, ethyl mercury is actively excreted via the gut unlike methyl mercury that accumulates in the body. Two independently-conducted epidemiological studies have been completed in the United Kingdom. These studies further support the safety of thiomersal-containing vaccines in infants in the amounts used in existing vaccines.

The FDA Center for Biologicals Evaluation and Research (CBER) offers a very comprehensive resource on thimerosal and vaccines.

In 2003, Geier and Geier claimed to have found a statistically significant association between thimerosal-containing vaccines and autism based on an analysis of data from the CDC's Vaccine Adverse Event Reporting System (VAERS). The American Academy of Pediatrics severely criticized the study for shoddy methodology and factual errors. According to the AAP:

The most important weakness of the article is the reliance on VAERS data to draw conclusions about adverse event associations or causality. VAERS is a passive surveillance system for reporting possible vaccine adverse events that depends on health care professionals, patients, and others to file reports. Health effects reported to VAERS as being associated with vaccines may represent true adverse events, coincidental occurrences, or mistakes in filing. Inherent limits of VAERS include incomplete reporting, lack of verification of diagnoses, and lack of data on people who were immunized and did not report problems.

Perhaps the best evidence against the thimerosal/autism hypothesis is the fact that banning thimerosal doesn't reduce autism rates. If thimerosal caused autism, you would expect autism rates to fall after the offending vaccines were stricken from the immunization schedule. Several nations including Denmark and Canada have already banned thimerosal-containing vaccines, but no declines in autism have been observed so far. In the United States, the FDA has worked with vaccine manufacturers to decrease thimerosal exposure in the standard infant immunization schedule by 95%. So far, decreased exposure hasn't translated into decreased autism incidence.

In my next post, I'll talk about the allegations of collusion, influence peddling, and data suppression. So far, I see no evidence of a conspiracy or a coverup. However, the evidence points to the usual combination public relations and influence peddling.


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Listed below are links to weblogs that reference Thimerosal: correlation, causation, and conspiracy:

» Thimerosal from Big Monkey, Helpy Chalk
Majikthise has a good post up on the Thimerosal/autism issue, following some harsh posts by Orac in response to this salon article. [Read More]

» The right and the left (for the moment, anyway) from Respectful Insolence
I've just noticed that my little screed against the RFK Jr. article on on the supposed mercury-thimerosal connection has been linked to from both the left and the right... [Read More]

» What causes (cont.)… autism? Makhloqet on mercury-based vaccines. from Quicksilver כספית: A commentary on rabbinic texts and toxicality

For criticism of the claimed link between autism and mercury (thimerosal) in vaccines, you might read a skeptical medical blogger (Respectful Insolence) a... [Read More]

» Evidence of Harm from Lean Left
Quite a bit has been made of Robert Kennedy Jr's article in Salon about the possible cover up of a link between mercury and autism. Majikthise, who does not think there is a link, has a very good round up of the issues. I am agnostic on this matt... [Read More]

» RFK ROUNDUP from Blissful Knowledge
Please click here for my disclosure statements relating to the subject matter of this post. After the Institute of Medicine... [Read More]


I read somewhere that the increase in autism diagnoses may be related to a decrease in mental retardation diagnoses. I don't know if that's true.

Also, I believe that people much more knowledgeable about this sort of stuff than I are pointing out that autistics have no signs of the sort of brain damage that mercury creates, which would be another reason to doubt the connection.

I tend to be excessively skeptical of these sorts of conspiracy theories, but I try to overcome that. Unfortunately, the Salon article half convinced me for half a day, because I trust Salon, and now I am even more set against conspiracy theories now that I realize I was "had." (Especially since I have three children born during the last ten years, all of whom were vaccinated, and I was more than half worried for that half a day, even though all are highly verbal and social. If one were sick, I don't know what I would have thought then.) Of course, very occasionally conspiracy theories turn out to be true, so my mental heuristic of distrusting them might lead me to some false conclusions.

I think it's very important for all of us to be aware of our mental narratives and seek to overcome that in the interest of the truth. Just because companies are greedy and and interfering with nature sometimes causes disasters, doesn't mean that these things are true in this case.

So, they put mercury in vaccines and the burden of proof is supposed to be on the consumer? Whether or not a statistical link to a specific neurological disorder can be proven, this seems like insanity to me. I work in a laboratory. If I spill even a miniscule amount of mercury on the floor of the lab, I have to call in a virtual hazmat swat team to deal with the "incident". Paperwork to fill out, etc. But it is perfectly OK to to inject it into your kids because you can't find a statistical correlation with a particular neurological disorder? Well, I don't have any kids. So I won't pass judgment. And clearly from a statistical point of view the benefits of immunization outweigh the risk of low levels of heavy metal contamination. But today it clearly is not an either or proposition. It is simply a bottom line decision by the drug companies and that is what is unconscionable.

New study links mercury to autism
Level of disorder dropped dramatically after element removed from vaccines
A new study shows a direct relationship between mercury in children's vaccines and autism, contradicting government claims there is no proven relationship between the two.

Published in the March 10 issue of the Journal of American Physicians and Surgeons, the data show since mercury was removed from childhood vaccines, the reported rates of autism and other neurological disorders in children not only stopped increasing but actually dropped sharply – by as much as 35 percent...

Early Downward Trends in Neurodevelopmental
Disorders Following Removal of Thimerosal-
Containing Vaccines
David A. Geier, B.A.
Mark R. Geier, M.D., Ph.D.
Download article in PDF format

More recent material than what you have linked to your postings above. The material you link Posted May 16, 2003 Study Fails to Show a Connection Between Thimerosal and Autism

...The authors claim falsely that children in the United States in 2003 may be exposed to higher levels of mercury from thimerosal contained in childhood immunizations than any time in the past, when in fact, all routinely recommended infant vaccines currently sold in the United States are free of thimerosal as a preservative and have been for more than 2 years (

that is disputed in recent studies as well

Early Downward Trends in Neurodevelopmental
Disorders Following Removal of Thimerosal-
Containing Vaccines
David A. Geier, B.A.
Mark R. Geier, M.D., Ph.D.
Download article in PDF format

Vol 2 No 1 Spring 2006

also see

Influenza Vaccine: Review of Effectiveness of the
U.S. Immunization Program,
and Policy Considerations
David A. Geier, B.A.
Paul G. King, Ph.D.
Mark R. Geier, M.D., Ph.D.
Download article in PDF format

Vol 2 No 3 Fall 2006

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