More evidence that mercury in vaccines doesn’t cause autism

Photo from UNICEF via flickr

A comprehensive study published today has failed to find any relationship between autism spectrum disorder (ASD) and the administration of vaccines that contain thimerosal. This lack of association even extends to prenatal exposure to thimerosal-containing vaccines. Will this study finally put an end to the manufactroversy about vaccines, thimerosal, and autism?


There’s been repeated claims over the past two decades that vaccines are responsible for causing autism. (A detailed backgrounder may be found here.) The incidence of autism diagnoses has climbed over the past two decades, and some have pointed to vaccines as the culprit – specifically, the mercury preservative used in most products.

Thimerosal has been a preservative in vaccines for decades. It is metabolized into ethylmercury and excreted by the kidneys in the urine. This may be contrasted with methylmercury, the mercury form for which exposure limits have been established by the US Environmental Protection Agency. In 1999, it was observed that children given routine vaccinations could have received more ethylmercury than the safe limit established for methylmercury. As a precaution, manufacturers were asked to remove thimerosal from vaccines, and it was further recommended that studies be conducted to evaluate the relationship between receipt of ethylmercury, and autism.

Previous studies have failed to identify any relationship between thimerosal and autism. And after thimerosal was removed from the majority of vaccines, the incidence of ASD hasn’t decreased. However, there hasn’t been a detailed analysis of the specific prenatal and post-natal exposure to thimerosal-containing vaccines. That’s what this trial set out to answer.

This study by Price et al, entitled, Prenatal and Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of Autism is a partner to a study by Thompson et al published in the New England Journal of Medicine in 2007, that examined the relationship between thimerosal-containing vaccines and adverse neuropsychological outcomes – but deliberately excluded ASD. Briefly, the Thompson study failed to find any relationship between the two.


Canadians brag a lot about their health care system, but this trial could probably have only been done in the USA, where there’s an electronic medical record to identify patients and and collect medical information. Three managed care organizations participated in a case-control study of 256 children with Autism Spectrum Disorder (ASD) and 752 controls that were matched for birth year and gender. Children were eligible to participate if they were born between 1994 and 1999, so children were 6 to 13 years old at the time of the study. ASD children were identified by searching databases for diagnoses relevant to ASD. Mothers were interviewed, and children were also directly assessed using standardized tools to confirm the diagnosis. Three groups were tracked: ASD; autistic disorder (AD) (a subset with more severe symptoms); and ASD with regression (AD-R) (children reported to have lost previously acquired language skills). Assessors were blinded with respect to the thimerosal exposure of the child and mother. Controls were screened via a maternal interview to ensure no children in the control group had undiagnosed ASD.

Each child’s history of thimerosal-containing injections (TCIs) was pulled from electronic immunization records. The mercury content of each vaccine received was determined by tracking the manufacturer and product lot, which was compared against manufacturer records. The mother’s receipt of immunoglobulins, tetanus, and diptheria-tetanus vaccines was also obtained from medical records. This allowed a calculation of the exact amount of ethylmercury administered.

Multiple covariates (variables that could influence the outcome) were also tracked, including child and family characteristics (mother’s age at birth, education level, income, birth order, breastfeeding duration, etc.); prenatal mercury exposure from fish, cosmetics, or dental fillings; use of tobacco and other drugs; and multiple child birth factors (e.g., respiratory distress, etc).


After exclusion criteria and patient refusals were applied, 256 children met the criteria for ASD, including 187 with AD and 49 with AD-R. Characteristics were largely identical between the children with ASD and the 752 children in the control group.

Children with ASD, and controls, had similar exposure to ethyl mercury over sequential time periods (see Table 2 of the study). The variation in mercury exposure was considerable in each group, due to factors that included receipt of vaccine, different brands of vaccines, and administration of vaccines individually or as combined products. Here are the pivotal findings:

  • Exposure to ethylmercury from TCIs either prenatally or in the first month of life was not associated with any form of ASD.
  • In older groups, higher levels of ethylmercury exposure were associated with a decreased risk of each of ASD, AD, and AD-R.

There’s no known mechanism by which vaccines with ethylmercury would reduce the incidence of ASD. The authors looks at different reasons for the difference, but found none. It could be that this is simply a spurious finding reflective of the observation that the two groups don’t really differ.


This detailed analysis found no relationship between ASD and thimerosal exposure. Limitations to the analysis include the fact that this is an observational study. While painstaking measures were taken to control for confounders, it’s always possible there’s a unknown confounder.

A prospective, randomized trial (vaccinated versus unvaccinated) will never be conducted as it’s not ethically permissible. Nor is it even possible anymore, as thimerosal has been removed from virtually all vaccines. This study is “as good as it gets” with respect to what an observational trial can do to address the thimerosal – autism question. The results add to numerous other studies which also failed to identify a link between thimerosal-containing injections and autism. It’s persuasive and compelling evidence, that there’s no relationship to be found.

Will the publication of this study stop antivaccinationists from claiming that thimerosal in vaccines causes autism? Of course not. More data won’t be persuasive, because the idea that thimerosal causes autism was never based on good evidence evidence to begin with. But this study gives science advocates further evidence to reassure those unsure of the safety of vaccines that there is no relationship between thimerosal-containing vaccines and autism.


Price CS, Thompson WW, Goodson B, Weintraub ES, Croen LA, Hinrichsen VL, et al. (2010). Prenatal and Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of Autism. Pediatrics, doi:10.1542/peds.2010-0309.

Free full-text of the study is available here.

21 Responses to “More evidence that mercury in vaccines doesn’t cause autism”

  1. Jeff Orchard says:

    Hey, higher levels of ethylmercury decreased incidence of ASD?!?! We should start a movement, “Fill your kids with Thimerosal to prevent autism… my daddy instinct says yes.”

  2. Randi says:

    No doubt this “study” was bought and paid for by a major pharmaceutical corporation interested in pushing vaccines. This is a really dangerous story that is misleading parents into vaccinating young kids.

    Shame on you all.

    • Erik Davis says:

      Actually, if you read the acknowledgments…it was funded by the Center for Disease Control. The CDC asked AHIP, a national association of health insurance providers, to orchestrate the research, and AHIP farmed out much of the work to Harvard & UCLA. Insurance companies are no friend of pharma…if anything, they’d have a pretty strong incentive to find a reason not to fund vaccines…yet they found the opposite.

  3. Mike says:

    What I’d like to know, is whether there is any actual benefit to having thimerosol, or aluminum, or formaldehyde or any of the other toxic items that you always hear about associated with vaccines. My understanding is that using these items allow the manufacturers to produce the vaccines more efficiently. So, we’re basically shooting our kids up with small amounts of neurotoxins so that the Mercks of the world can have larger profits? I really don’t get why the medical industry works so hard to defend this practice. Is the pharmaceutical industry really not capable of delivering vaccines that are free of any type of neurotoxin?

    The science based folks go through so much trouble to demonstrate that none of these neurotoxins are having any measurable effect on children. Couldn’t the money/effort being spent on that endeavour be better spent in actually trying to create vaccines that don’t contain any type of poison? An even better suggestion would be to try and discover the mechanism behind the encephalopathy that some children develop after receiving a vaccine, and trying to screen children so that the higher risk ones can avoid ending up like Hannah Poling or the various others that the US govt is now compensating for the devastating effects that vaccines have had on them.

    (Notice that the word ‘autism’ doesn’t appear anywhere in my post. And I’d like to keep that word out of any discussion that my comment above may spark).

    • Making a manufacturing process less efficient is, by definition, money that is not better spent. Doubly so when you consider that inexpensive medication can be the difference between life and death.

      It’s an especially bad suggestion, because there’s no poison in the vaccines to begin with.

  4. Mike says:


    So then you would agree that the decision in 1999 to ask manufacturers to remove Thimerosol from vaccines resulted in the death of some children by driving up the cost of vaccine production? And not only did it kill some children, but it was a stupid idea in the first place because thimerosol is not the kind of thing we should be trying to avoid whenever possible?


    • I don’t know if any children died directly as a result of that decision. But if it caused an increase in the price of vaccines (which I’m pretty sure it did) without providing any medical or safety benefit (it didn’t), then it was a bad decision.

      We’re getting less of a result and we’re paying more for it. That’s not efficient public policy, and it isn’t an efficient business model.

      • Mike says:

        I guess I’ve never looked at it that way. Your comments make a lot of sense. I guess it’s too bad they’ve removed Thimerosol from most vaccines. Maybe we should consider re-adding it to all childhood vaccines. Maybe we can even double or triple the amount in each shot. If it could reduce the price of vaccines, and injecting a newborn with Thimerosol is nothing to be afraid of, then why haven’t we considered this?

        Since the Mercks of the world raised the price of their end product when they had to remove Thimerosol, then presumably they would drop the price of their products if they introduced it back in. Perhaps more Thimerosol could reduce vaccine prices even more. And if there were some more preservatives they could toss in there to bring their manufacturing costs down even more, think of all the extra lives we could save.

        After all, if they can openly admit their products cause brain damage in certain individuals, and no one seems interested in finding out why, they seem to be passing up a golden business opportunity to drop their bottom lines even more.

  5. Art Tricque says:

    Just heard a news item on Toronto’s 680 News radio station about the “new” book by Olmstead and Blaxill, with live quotes from Blaxill and a reference to Age of Autism. Most egregious, and thank goodness that it doesn’t seem to be on their web site — maybe yet. Nevertheless, please contact the station at 416-872-6800 to complain about this irresponsible journalism.

  6. Rob Tarzwell says:

    Mike, are you seriously suggesting that vaccine manufacturers deliberately and maliciously put deadly neurotoxins in vaccines?

  7. Mike, it doesn’t follow that because using a specific preservative can result in a cheaper manufacturing process, that using more of that preservative will cause the price of vaccines to fall. But I suspect you know that, and are no longer trying to make a serious point.

  8. Mike says:

    Let me first state the assumptions I’m making. I agree that if these assumptions are incorrect, then my argument falls apart.

    1) Thimerosol is a neurotoxin
    2) Referring to Thimerosol as ‘poison’ is reasonable.

    If someone wants to correct my assumptions or point me to some data showing some of the benefits Thimerosol can have for a newborn baby, please do.

    Rob : Am I saying that Thimerosol is added to vaccines deliberately? Of course it is. Did you think it ended up in there by accident?

    Was it added maliciously? I would sure hope not. I’m not accusing the vaccine makers of being malicious. I’m accusing the medical industry of not being critical enough of their shortcomings.

    Mitchell : One the one hand, you’re saying that you fully endorse the idea of adding a neurotoxic preservative to vaccines if it can reduce manufacturing costs. And on the other hand, your graphic is implying that its ridiculous to think the vaccine makers would add anything bad to their products just to make more money. Which opinion would you like to choose as your final answer?

    I get the impression that if I said the sky was blue, you’d be looking for some way to try and riducule that statement too.

    It amazes me to what lenghts people want to go to defend and rationalize every decision made by the pharmaceutical industry. The vaccine makers themselves admit that their product causes brain damage in certain individuals, and yet you never hear anyone in the scientific community admitting that this is a problem that warrants serious attention.

    • Scott Gavura says:

      Mike, dose is a critical factor you should add to your assumptions. Mercury is toxic in certain forms and doses. So is acetaminophen (Tylenol). So is nutmeg. So is iron, for that matter, which we actually need to ingest. But at at appropriate doses, none are poisonous.

      There’s no evidence that thimerosal in vaccines is acting as a neurotoxin.

      So getting back to your initial question on “is there a benefit” to thimerosal? This technical report from the World Health Organization discusses thimerosal elimination, reduction or replacement in vaccines. They point out that it’s not a simple matter of removing it:

      The primary role of thiomersal in vaccines has been considered to be that of a preservative, but data indicate that there are other effects of this additive on vaccine antigens which need to be taken into account if consideration is being given to its elimination, reduction or replacement. Indeed, in some production processes thiomersal is used in the inactivation of vaccine antigen along with heat, for example in the case of whole cell pertussis vaccine. Should a national health authority or a manufacturer decide to eliminate, reduce, remove or replace thiomersal in vaccines, then the strategy chosen may affect not only the subsequent ability of microbial contaminants to grow in vaccine preparations, but also vaccine quality, safety and efficacy. The question therefore arises as to what evidence is needed to ensure that a vaccine where the thiomersal content has been altered will be as safe and efficacious as the already licensed product.

      The different vaccine manufacturers have now addressed the technical and evidence issues. Despite the lack of any evidence of harm of thimerosal in vaccines, it’s largely gone from vaccines now.

    • “Mitchell : One the one hand, you’re saying that you fully endorse the idea of adding a neurotoxic preservative to vaccines if it can reduce manufacturing costs. And on the other hand, your graphic is implying that its ridiculous to think the vaccine makers would add anything bad to their products just to make more money. Which opinion would you like to choose as your final answer?”

      If you take out the word ‘neurotoxic’, then yes — that would be accurate.

  9. Michael Kruse says:


    You are also ignoring the fact that IF thimerisol is a neurotoxin – and you would have to produce evidence that it is, because I believe this has never been proven – that it is not a neuro-toxin at the levels encountered in a vaccine. Most poisons have a threshold below which they are considered non-toxic and the EPA and Environment Canada set acceptable exposure levels of the substance, based upon current evidence of potential harm. The benefit of adding thimerisol to multi-dose vials – eliminating fungus growth and the potential of a quite harmful fungal infection – far outweighs the risk, if any, of exposure to thimerisol at the levels encountered in a vaccine.

    This debate has nothing to do with defending the pharmaceutical industry. It has everything to do with defending the scientific process and the findings of many studies that have shown no link between thimerisol and brain damage, including autism.

    Your straw man of “no one wants to know why vaccines cause brain damage” is simply bad logic. The safety of vaccines is paramount and they have been studied more than any other individual treatment in the history of medicine. Harm reduction is at the heart of public policy for the regulation of medicine. It would be disingenuous to say that we can prove something is 100% safe: this is not how science works. There is a constantly updated risk/benefit analysis and with new data comes new guidelines for therapy with the goal of a safer, more effective process. This has shown itself to be a very successful way to run public health, and those who cry conspiracy without data are adding uncertainty into a problem unnecessarily which ultimately has a negative impact on the health of children.

  10. Mike says:


    I don’t necessarily agree with your acetaminophen/nutmeg/iron analogy as those are all things that we actually want to ingest at certain does, whereas Thimerosol is something you would generally try to avoid whenever possible. However, I hear what you’re saying. You’re saying there’s no evidence suggesting the dosage of Thimerosol in vaccines is dangerous enough to warrant trying to remove it. And I appreciate your technical insight. For me, if a small amount (small enough to be considered harmless by the powers that be) of rat poison (or something similar) was beneficial to the production of infant formula, I would still want to see the makers of infant formula use their innovation to find ways of producing it without using rat poison. I would generally want my newborn infant to ingest as little of that type of stuff as possible. But I guess that’s a matter of personal preference, and not necessarily a “defensible” opinion in the scientific sense.


    Since the safety of vaccines has been studied more than any other individual treatment in the history of medicine, can you let me know how close we are to understanding the mechanism behind vaccine-induced brain damage so that we can identify the children most at risk?

    • Scott Gavura says:

      Hi Mike – I think what you’re saying is entirely understandable. Why wouldn’t we want to avoid something, even potentially harmful, if we have the choice? One thing to keep in mind is that it’s impossible to avoid the consumption of mercury. Even in the absence of industrial pollution, mercury is an element and is found in the environment, in the form methylmercury. We all have it in our bodies – it’s even in breast milk. Breastfed children will absorb more than twice as much mercury from this route, than was ever in all vaccines combined. And keep in mind that the mercury in vaccines is/was ethylmercury – it does not accumulate like methylmercury. But you don’t see mass calls for breastfeeding to end.

  11. Mike: do you eat fish?

  12. Mike says:


    If you’re looking to pick fights or head off-course down some other tangent, I’m not interested. I realize there are harmful elements to much of what we regularly consume. If you want to make a serious attempt to address some of the questions I’ve raised, similar to what Scott did, I would welcome that. Otherwise, I’m sure we both have better ways to spend our time.


  13. Richard says:

    What you don’t understand is that it isn’t Mercury alone that causes it. It is a Fact that Low-Level Mercury poisoning from any source can cause the symptoms of autism to appear but an underlying condition must also be present or else there would have to be additional sources of Mercury in the environment.

    I speak from experience on this. When I was 2 and a 1/2 I was diagnosed with “Pervasive Developmental Delay” and was later Diagnosed with Autism. However, in my case, I don’t really have Autism. Just the symptoms of Mercury poisoning that are identical to Autism along with other more serious problem. I am getting treated as an adult and am recovering.

    No one can say that my case wasn’t from the Vaccines. However, neither can anyone say that the vaccines alone caused it. The morning sickness drug Bendectin caused an Epigenetic change which affected the body in some unknown way (still have a series of tests to do) but it seems that some combination of things resulted in the Mercury having more of an affect than it should have.

    Anyway, on this I speak from the perspective of an adult who was a child with “Autism” who developed symptoms after being vaccinated. There are still allot of unanswered questions but the vaccines were a contributing factor.


  • Scott Gavura

    Scott is passionate about improving the way drugs are used. A pharmacist by background, Scott has a professional interest in improving the cost-effective use of drugs at the population level, while helping consumers make more informed decisions about their health. He blogs about pharmacy practice and questionable science at Science-Based Pharmacy and Science-Based Medicine. All views expressed by Scott are his personal views alone, and do not represent the opinions of any current or former employers, or any organizations or associations that he may be affiliated with. All information is provided for discussion purposes only, and should not be used as a replacement for consultation with a licensed and accredited health professional.