More Evidence for the Safety of Vaccines

29 Sep

This article was originally published at the NeuroLogica Blog and is re-published here with permission.

By Steven Novella, MD
NeuroLogica Blog

A new study just published in the New England Journal of Medicine, Early Thimerosal Exposure and Neuropsychological Outcomes at 7 to 10 Years, does not support a correlation between mercury in vaccines and neurological damage. It adds to the growing evidence that vaccines are safe and they do not cause neurological disorders. This study did not look at autism (a study that will be published next year looks, again, at vaccines and autism), but the mercury-causes-autism crowd are still unhappy with the results.

I have been following this issue closely for several years. Although my awareness of the issue goes back much farther, I started to seriously research the claim that the MMR vaccine, or that thimerosal in other vaccines, causes autism while researching an article on the topic for the New Haven Advocate. As a physician (a neurologist) and a skeptical activist I knew I had to get this issue right. I certainly did not want to falsely stoke the flames of public fear, nor did I want to cast myself in the role of denier.

Early on in my research I really did not know which way I was going to go with the issue. Should my bottom line be that there is real reason for concern here, that there is nothing to the claims, or that we really don’t know and will have to just wait for further research? But after reading through all the claims on both sides, and all the research, it was an easy call – vaccines, and specifically the MMR vaccine and thimerosal, do not cause autism, and the alleged autism “epidemic” is likely just an artifact. Those claiming there is a connection were drowning in conspiracy thinking, logical fallacies, and blatant pseudoscience. Meanwhile every piece of reliable clinical data was pointing in the same direction – no connection.

But still, while I was confident in my final conclusion, a small connection between mercury and autism that eluded the existing data could not be ruled out. Or perhaps there was an angle to the whole story that we were missing but would later come to light. I have had enough experience with scientific medicine to be humble in the face of the complexity of medicine and biology. The only rational position is to remain open to new data and new ideas. On this issue there was sure to be more studies in the future – and the ultimate test of the thimerosal-autism connection, the removal of thimerosal from the vaccine schedule, was yet to be seen. So I confidently plunked my nickel down and waited for the future to unfold.

Everyone likes being right, and sometimes this desire clouds our judgment. I have learned, therefore, how to cheat, which is to say how to always be right. All you have to do is say that your position is based upon the existing data, but is contingent upon the results of future studies. In other words, the “right” position is to change your final answer to accommodate new evidence as it comes in. Therefore the only “wrong” answer is to stick to your original position despite new evidence that contradicts it.

OK – so this is just restating how science is supposed to work, but it is amazing how many people forget to cover their behinds with this simple rule. Usually this is because they are not doing science – they are taking an ideological position, and ideology is inflexible. This is a huge advantage for science over ideology, and why, when science and ideology clash, science is almost always right.

In the case of vaccines and autism, since writing my first major article on the topic, the data has come in all consistent with my original position (so I get to be doubly right). Removing thimerosal from vaccines did not decrease the incidence of autism (or decrease the rate of increase in new diagnoses). And several new major studies came out all showing no association – not counting the utter crap being produced by the Geiers.

Enough had happened to warrant an update, so I jumped at the chance when Ken Frazier of the Skeptical Inquirer asked me to write an article on the topic. My article will be out in the next issue, along with a couple of smaller ones on the same topic, so take a look.

Alas, as is often the way in the world of science, my paper is outdated before it even goes to print. This new study, of course, will not be covered in the article. But that’s what blogs are for – instantaneous news and analysis.

Actually, several of my fellow science bloggers have already beat me to the punch. They cover the article, and the response to the article by the mercury crowd, in great detail, so I will not duplicate it here.

Orac at Respectful Insolence goes over the press release of A-CHAMP (one of the mercury militia) that attempts to dismiss the study. He shows that, while the study (like all studies) has its weaknesses, it does add significantly to the body of evidence showing that vaccines are safe. The complaints of A-CHAMP are either wrong, overblown, or inconsistent with their prior positions and shows that they are just trying to tear down the study at all costs.

For the record, I agree with Orac that the study is good enough that it’s conclusions add to the cumulative data on this topic, and that the weakest element of the study was the 30% compliance rate. In other words, only 30% of the subjects that they looked at for the study made it into the final analysis. This opens up the door for selection bias. Orac is probably correct that this bias would likely overestimate a correlation, not underestimate it, but you can never be sure with such things.

I will add that the 30% figure is not as bad as it first seems. The study reports:

Of 3648 children selected for recruitment, 1107 (30.3%) were tested. Among children who were not tested, 512 did not meet one or more of the eligibility criteria, 1026 could not be located, and 44 had scheduling difficulties; in addition, the mothers of 959 children declined to participate. Most of the mothers (68%) who declined to participate in the study and provided reasons for nonparticipation cited a lack of time; 13% reported distrust of or ambivalence toward research. Of the 1107 children who were tested, 60 were excluded from the final analysis for the following reasons: missing vaccination records, 1 child; missing prenatal records, 5; missing data regarding weight, 7; and discovery of an exclusionary medical condition during record abstraction, 47. Thus, 1047 children were included in the final analyses. The exposure distribution of the final sample was similar to the exposure distribution of the initial 3648 children selected for recruitment in the study.

So about 40% of those that did not make it into the final analysis simply could not be located – this is unlikely to represent a bias. But this is a small point.

Isles from Left Brain/Right Brain points out that Sallie Bernard (a believer in the mercury hypothesis) was consulted on the study design and execution and did not criticize its methods until after the results came back negative. That kind of behavior instantly sacrifices all your credibility in the science club.

Kristina Chew at AutismVox reiterates what I did above – that the mercury-causes-autism ideologues are always asking for more studies, but refuse to change their position when the studies they ask for come out. They are waiting for studies that show what they want them to show – we call that “cherry picking.”

The other side is busy too. David Kirby (a bad journalist who desperately wants to be a bad scientist), who wrote the book Evidence of Harm, published an article online in that absolute rag, The Huffington Post (to be fair, they also published this piece by Arthur Allen defending the paper’s conclusions). Kirby repeats all the same points in the A-CHAMP press release, but he emphasizes the fact that the study found some neurological symptoms that were higher in the subjects who received more thimerosal. Kirby proceeds to completely misinterpret the significance of this.

The study looked at 42 different outcomes, and set the p-value for significance at 0.05. A vague concept of basic math should be sufficient to see that some outcomes will reach significance by chance alone. The researchers arguably should have adjusted their statistics to account for the fact that they were looking at 42 variables – but instead they just looked at all the outcomes that were significant to see if there were any patterns or trends. What they found was that there were a few scores that were worse among those exposed to more thimerosal, but there were also a few scores that were better. There was a random distribution of positive and negative effects that essentially average out to no net effect. It’s all just noise. (Is there a small signal hiding in the noise? There could be – scientists have to be honest about that. But that doesn’t mean there is.)

What Kirby does is not just really dumb, it’s despicable. He cherry picks all the negative (meaning bad) neurological outcomes and pretends that the study shows a correlation (it doesn’t, when you look at ALL the data). He then tries to dismiss the positive (good) outcomes as absurd. He mockingly writes:

If they (the CDC) really mean that thimerosal increases IQ levels in males, then sign me up for a double-dose flu shot this year.

No, David, they don’t mean that. Not by any stretch of the imagination. It takes incompetent statistical analysis or the blindness of ideology to write something so ridiculous. What the CDC means is that the study does NOT show that thimerosal increases IQ, nor that it causes motor tics, or improve motor skills, or decrease language skills, or anything else. The study showed no correlations because it all averaged out as noise.

This is, by the way, the same mistake that astrologers make (remember that crusty pseudoscience?). They look at many variables then cherry pick the outliers. At best what this study might show is a possible correlation, but any such possible correlation would have to be corroborated by a later study (with fresh data) that looked specifically at that one variable.

So the pattern that I found when I first started looking at this issue – that all the reliable data was on the side of no correlation between vaccines or mercury and autism or neurological disorders – continues to hold up to new data. The other pattern I noticed – that those promoting a correlation were relying on bad science, logical fallacies, and ad hoc conspiracy claims – also continues to hold.

In the last few years every new study showed no correlation, and the mercury militia responded with abject nonsense and dismissal. This cycle seems to be repeating itself over and over, and this latest study is no exception.

21 Responses to “More Evidence for the Safety of Vaccines”

  1. Joseph September 29, 2007 at 19:28 #

    The exposure distribution of the final sample was similar to the exposure distribution of the initial 3648 children selected for recruitment in the study.

    As I was telling Swartz, this is a key indication that there was no selection bias. It’s really what matters. Even if the distribution of the outcomes was different in the two groups, an effect should’ve been detected if there was any.

  2. Ms. Clark September 30, 2007 at 00:06 #

    Kirby really is despicable, and I think he’s a paid mouthpiece, too.

  3. Toad September 30, 2007 at 00:17 #

    “If they (the CDC) really mean that thimerosal increases IQ levels in males, then sign me up for a double-dose flu shot this year.”

    Okay, it’s an artifact. But -if- it were true, would a double-dose be enough?

  4. Kristina September 30, 2007 at 02:38 #

    It really is becoming a neverending cycle—-no argument, no amount of evidence, no patient analyses can convince. Parents who continue to believe these theories (of a vaccine-autism link, for instance) only become more caught up in finding biomedical explanations and treatments—I am seeing a friend caught up in this now—I don’t know where it will end.

  5. Kev September 30, 2007 at 03:27 #

    It won’t end unfortunately. We will see a continual and escalating cycle of an increase in vaccine preventable disease, we will see more and more autistic kids being experimented on by their parents and their parents pet quacks leading to more injuries, hospitalisations and deaths. We will see less and less research monies going into education, housing and adult services, or into researching valid evidence-based interventions as these assholes get louder and louder.

  6. Do'C September 30, 2007 at 03:45 #

    The prospect of your prediction coming true is irritating to say the least, Kev. Great article Dr. Novella.

  7. Matt September 30, 2007 at 04:15 #

    Sorry Do’C, but it gets even more irritating.

    Kev may be assuming that the funding stays flat. We have to consider that funding will go down. Just like JM just had her flash in the pan, autism may not be the darling of the disabilities that it is today. Add to this the annoyance of the public and the governments when the final nails are hammered into the mercury coffin. When our good colleagues at GR and SafeMinds, etc. still don’t accept reality, the funding groups will realize that the mercury mom’s may not have always worked in good faith.

    Please tell me where this logic falls apart.

  8. Ms. Clark September 30, 2007 at 06:12 #

    I see the funding agencies and donors in general getting really ugly and not funding autism anything anywhere as a backlash against the egomaniacal and litigation driven insanity of SAFEMINDS and GR, NAA, ARI, No Mercury, MAM and their buddies. Even ASA has put it’s lot in with the nutjobs. GR is doing it’s best to maintain one foot in the wingnut world and one foot in a more rational world… they are hemorrhaging credibility, in my opinion.

    And who will be the losers? The autistic adults and kids, and the kids’ parents.

    The biomed/epidemic criers are like a thousand idiotic little boys who have cried “Wolf!”, too many times.

  9. Schwartz September 30, 2007 at 06:43 #

    Well written!

    The only surprising thing is that you thought the 30% was the weakest factor.

    I was OK with that number, but the weakest parts I see are the small number of participants in the zero-low Thimerosal exposure, the limited scope of the results given the large number of exclusions, and the large amount of time passing between initial exposure and measurement (7 years).

    It would certainly indicate that increasing amounts of mid-level exposure to Thimerosal has no long term noticeable impact on Neurological problems.

  10. Joseph September 30, 2007 at 13:06 #

    The 30% thing has been overplayed. What matters is not the participation so much as how representative the participants are compared to the whole group.

    It could be 1% participation, but if it’s representative and the number of participants is big enough to be able to draw statistical conclusions, then it’s a good group.

    I’d even argue that it doesn’t have to be completely representative. The exposure distribution is what really matters.

    To compare to the GR phone survey, for example, vaccination vs. no-vaccination could not have been distributed evenly across respondents and non-respondents; and that’s the major problem with that survey. I don’t care too much if 95% hung up the phone.

  11. John Fryer September 30, 2007 at 17:19 #

    Hi Stephen,
    I stopped at you: ‘Wanting to get it right.’
    If you can’t see that the most deadly brain nerve destroying toxic chemical cannot be at fault when it is at more than 10 000 times the danger level then have a chat with me.
    john fryer at orange dot fr
    And perhaps I might learn how to spell your name correctly.
    John Fryer Chemist

  12. Toad September 30, 2007 at 17:38 #

    “If you can’t see that the most deadly brain nerve destroying toxic chemical cannot be at fault…”

    I can see that it cannot be at fault.

  13. Joseph September 30, 2007 at 19:18 #

    it is at more than 10 000 times the danger level

    As explained to you previously, it’s not at 10,000 times “the danger level.”

    I can assure you, 0.0025 micrograms of mercury is not a dangerous level.

  14. John Fryer October 10, 2007 at 20:11 #

    Hi Joseph
    I think I agree with your post:
    0.0025 micrograms is not at a dangerous level.
    But 25 micrograms is at a dangerous level and that is in many vaccines used on underweight babies at age 1 day and often not well.
    This amount is exactly 10 000 times as much as you quote is a safe amount.
    I don’t know if it makes a few children autistic but I am positive it kills some infants.
    Harry Clark got his 25 micrograms at 4pm and was dead at 10 pm the same day. He was 8 weeks old and fit and well before the injection.
    I don’t know how many examples like this it takes to prove a point?
    There were 2 000 such deaths every year in the UK alone when they used mercury.
    Mercifully the SIDS today is many times less and the mercury is too.

  15. John Fryer October 10, 2007 at 20:21 #

    Hi Toad
    You think a brain destroying chemical is ok?
    I am sure you don’t. But you don’t need to inject it. Karen Wetterhahn got some on her gloves and an almost negligible amount got through her unbroken skin and she was fine for months afterwards. But she died in about one year despite the chelation and monitoring of the mercury in her body.
    The autopsy showed 1 ppm.
    The mercury in vaccines is at 5 000 ppm.
    In the USA more than 100 000 infants have died from unexplained causes shortly after receiving mercury containing vaccines.

  16. notmercury October 10, 2007 at 23:58 #

    John, at least try to get your facts straight. She was exposed to dimethylmercury which is nothing like thimerosal. It passed through her gloves which would never happen with thimerosal, ethylmercury, or even (mono)methylmercury. Doesn’t your title imply some basic training in chemistry?

    Karen Wetterhahn’s blood concentration was something like 5,000 mcg/L which is not exactly 1ppm. Nor could you compare the concentration of mercury in a vaccine to the concentration in her bloodstream.

    Would you like to argue that she died before she became autistic?

    If thimerosal causes autism, because it is a brain destroying chemical, as you suggest, where is the evidence of brain destruction in autism? Where is the loss of muscarinic receptors that is nearly universal in cases of actual mercury poisoning?

  17. Matt October 11, 2007 at 00:16 #

    Oh no, the “mercury is toxic” red herring.

    Let’s discuss the toxicity of mercury on an autism blog. That way, autism and mercury are assumed to be related. That way, you can make people look mean for defending a toxic material.

    You don’t have the science to back up your real claim, autism and mercury are linked, so you fall back on the tried and true Kirby/mercury-mom debate trick.

    You can spin your wheels all you want on different forms of mercury and toxicity, but it will never make up for a lack of scientific evidence about it’s link with autism.

  18. HN October 11, 2007 at 00:24 #

    John Fryer said “In the USA more than 100 000 infants have died from unexplained causes shortly after receiving mercury containing vaccines.”

    Do you have any real documentation for that statistic? Remember not to use the VAERS database, as that is just reports without any verification.

  19. Matt October 11, 2007 at 00:46 #

    John Fryer said “In the USA more than 100 000 infants have died from unexplained causes shortly after receiving mercury containing vaccines.”

    Ah, the “muddy the water” technique.

    Make bold statments. Some fraction of the readers will say, “I’m confused. I will take the ‘safest’ route. Since everyone else vaccinates, I can skip it, right?”

  20. HN October 11, 2007 at 05:23 #

    John Fryer, why don’t you ever post any references or documentation?

    Where do you get your information? Why should we believe you?


  1. NeuroLogica Blog » More Evidence for the Safety of Vaccines - September 29, 2007

    […] blog entry was reprinted with permission over at Left Brain/Right Brain, so there may be some more comments over […]

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