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Capitol Hill Update: "Weaknesses and Limitations" of the CDC's Vaccine Safety Database

DavidkirbyBy David Kirby

There has been much discussion – and some confusion – about a letter sent earlier this year from CDC Director Dr. Julie Gerberding to Congress, in response to a report by a panel of the National Institutes of Environmental Health Sciences (NIEHS) that detected many weaknesses and limitations with the CDC-run Vaccine Safety Datalink (VSD).

In her letter, Dr. Gerberding wrote that “CDC concurs” that the weaknesses and limitations inherent in the database would call into question the usefulness of using the VSD for conducting ecological and other types of studies on the potential association between thimerosal exposure and autism risks.

It has been my contention that the same weaknesses and limitations that reduce the usefulness of VSD-based ecological studies going into the future, would likewise have negatively impacted the study already conducted by Thomas Verstraeten, which was a retrospective cohort study, and not an ecological one.

During my briefing in Washington on September 24, I mentioned the NIEHS report, and included the CDC agreement with the findings, without explaining the important distinction between an ecological study and a retrospective cohort study.

During the Q&A session, a Congressional staff person asked me about this, and suggested that I had tried to conceal information and thus deceive people in the room. This was not my intention.

On Tuesday, September 30, I sent that staff person the following letter, which reprises and expands upon the answer I gave in person on the 24th.

I have decided to reprint it here, because I think it is important to note that Dr. Gerberding did indeed concur with findings of “limitations and weaknesses” within the VSD database which would negatively impact ecological studies going into the future.

These problems woud ALSO impact other VSD-based studies (i.e. Verstraeten) conducted in the past. Sadly, but perhaps not surprisingly, Dr. Gerberding in her letter to the powerful House Appropriations Committee, utterly failed in her duty as CDC Director to address, or even respond to, the most serious and important finding in the NIEHS report. Namely, that the fundamental “weaknesses” within the VSD itself “reduce the usefulness” of the VSD to study thimerosal and autism. Period.

This is important, of course, because the Verstraeten study was a cornerstone of the 2004 Institute of Medicine report, which found no evidence of a link between thimerosal and autism. It remains a pillar of medical opinion to this day, despite a letter from Verstraeten himself, published in Pediatrics, insisting that his study found no evidence AGAINST an association, and was in fact a neutral study, and that indeed, more research was recommended.

Here is the letter. I will let readers know when I get a reply:

SEPTEMBER 30, 2008

Thank you for attending the Congressional briefing on Autism on September 24. I was glad to see that you took the time out of busy week to listen. I also appreciate your question about the NIEHS report on the VSD database, HERE and Dr. Julie Gerberding’s response to the House Appropriations Committee.

As you rightly pointed out (and as I concurred that day) I omitted an important detail in regards to Dr. Gerberdings’s letter to the Committee. I regret that, and never meant to mislead people in the room.

It was a rather artless sin of omission.

I think the lesson for me here is that, when you try to cram a two hour presentation into 25 minutes, it is wise to not include very complicated and, as you put it, “somewhat arcane” details that are difficult to explain in such a short period of time. In retrospect, I probably should have focused solely on the NIEHS report itself, and left the Gerberding letter out of the presentation entirely.

That said, I still assert that the NIEHS report was very much germane the Verstraeten study, because it indentified, (as I said in my response to you on Wednesday), serious structural weaknesses inherent in the database, which might impact any type of VSD-based study to determine the risk of autism, if any, associated with thimerosal exposure.

The NIEHS panel’s mission, essentially, was twofold. The first was to evaluate the database itself for strengths and weaknesses for doing thimerosal/autism studies of any kind. The second, (broken down into specific ideas) was to evaluate the feasibility of using the database for certain studies, including ecological ones, going into the future.

As I interpret things, the panel concluded that the database itself suffered from several weaknesses and limitations, which in turn reduced its usefulness for studies of autism risks from thimerosal (ie, Verstraeten) AND ALSO reduced the feasibility of future studies (ie, ecological ones) that are based on data collected within the VSD.

In the NIEHS report, there was a charge to the panel that listed five distinct tasks:

1)  Identify the strengths and weaknesses of the VSD for evaluating the possible association between exposures to thimerosal-containing vaccines and AD/ASD

2) Advise NIEHS and CDC on the feasibility of a new VSD study to compare autism rates before and after removal of thimerosal from most US childhood vaccines, using an ecologic study (an epidemiologic design where there is no linkage between individual-level data on exposure and health outcome)

3) Identify any other uses of the VSD or other existing resources that might be used to examine an association between thimerosal and AD/ASD.

4) Develop recommendations for design, conduct, analysis and oversight of any proposed study.

5) Discuss the potential impact of possible VSD-based studies in the context of what is already known about autism and ASD.

In the “Report of the Panel,” the experts convened by NIEHS addressed Task #1 at the very beginning, and then went on to provide details of limitations and weaknesses, in the context of potential future (ie, ecological) studies.

The panel wrote: “Despite these overall strengths, the panel identified several areas of weakness. The cumulative effect of these weaknesses was judged to reduce the usefulness of the VSD for addressing the potential association between exposure to the vaccine preservative thimerosal and risk of AD/ASD. The weaknesses of primary importance are summarized below.”

Again, I interpret that to mean that the VSD itself suffers from limitations and weaknesses, regardless of what type of thimerosal-autism study it might inform.

Unfortunately, in her letter to the Committee, Dr. Gerberding chose to ignore this very serious first finding, and instead addressed the other concerns about using the VSD for ecological and other types of investigations.

Even so, Dr. Gerberding did concur that many of the weaknesses cited by the panel (for example, under-ascertainment of cases, changing business practices, differing diagnostic codes, and no accounting for prenatal and background mercury exposure) would reduce the usefulness of the VSD in conducting ecological studies of thimerosal and autism risks.

My point (and terribly made, I admit) was that Dr. Gerberding agreed that the VSD database contains many limitations and weaknesses, making it less than useful for doing ecological studies. However, these same problems would have, and indeed did, affect the Verstaeten study.

Finally, Dr. Gerberding wrote that CDC does not conduct ecological studies using the VSD. Instead, she (falsely) stated that CDC uses chart reviews, neurological follow up exams, and parental interviews in all VSD-based thimerosal studies.

The problem is, Verstraeten had no parental interviews and no neurological follow up exams. And there was very limited chart review: The investigators reviewed the carts of roughly 1% of the kids in the study.

So even though Verstraeten was not an ecological study, it did suffer from some of the same weaknesses that would impact an ecological study. The weaknesses that the NIEHS found within the database, and to which the CDC admits, call into question the validity of the Verstraeten study – again, in my opinion.

This is, indeed, arcane. And it is why I urged everyone to watch the DVD of my NYU talk, for a more thorough explanation. I have no reason to deceive people. I know that credibility means everything in this discussion, and I try to protect my own as much as possible.

I enclose a link to my remarks on this subject at NYU (which has also been added to the transcript on Age of Autism) HERE.

And HERE is a link to my Huffington Post piece on this issue, which as you can see, I corrected (the next day) in bold at the top of the piece.

Finally, I would very much like to speak with you on the phone, and go over the NIEHS report, to see if you interpret it differently than I do. Perhaps you can convince me that the inherent weaknesses in the database (to which Dr. Gerberding admits) are in no way applicable to the Verstraeten study. I promise to keep an open mind!

Many thanks, again, for attending the briefing, and for your thoughtful and detailed approach to this discussion.

Very respectfully yours,

David Kirby


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Well said. Thank you.

According to the USEPA methyl mercury web page organic mercury in the form of dimethyl mercury is lethal to touch.
"Limited information is available on absorption via inhalation and dermal routes. There is one reported human dermal exposure when a 48-year-old chemistry professor inadvertently spilled drops (0.4-0.5 mL) of dimethylmercury from her pipette into her latex gloves. Penetration of dimethylmercury through the gloves occurred instantaneously. Mercury hair level was elevated to almost 1,100 ppm, with a half life of 74.6 days. Five months after exposure, the woman experienced severe neurotoxicity and died 9 months later (Blayney et al., 1997; Nierenberg et al., 1998)." See
And according to Smith for methyl mercury “On the cellular level there is no ‘threshold point.’” (Smith and Smith, 1975).’” (Source: Dr. Edward Laws, Aquatic Pollution, 1993, p. 370).

It does not appear that the CDC and FDA cite any research that shows no brain tissue damage “on the cellular level” from so called “trace levels” up to 299 nanograms of mercury in vaccines? These are levels for which they say “This product should be considered equivalent to thimerosal-free products.” And if they can not cite any research then they should have the scientific integrity to “give all of the information” and say that they don’t know - rather than convey the “implication” that mercury in vaccines is safe.

sdtech, David, and to all, really:

Sdtech, you say, "Likewise in public policy, the CDC, AAP, and FDA should 'give all of the information.' Instead they convey the 'implication' that vaccines are safe. The question of 'is it safe' has NOT been answered."

Oh, but it has been answered, and the answer is, "No."

In fact, the question has been answered, buried, answered again and again, and buried again and again, because WE DON'T LIKE THE ANSWER.

I won't even begin to list--once more, since it's been done repeatedly--all the studies that have been done *since* Verstraeten, which do show a link between neurotoxic mercury and brain damage, including autism, because many links to such studies can be found if you look.

There are links right here in the archives of AOA.

But let's just mention what you, yourself, point out, sdtech, about the Verstraeten study: if half of the study shows a risk of autism, and the second half of the study fails to duplicate that, you still have "evidence of a link" (your phrase) if not absolute proof.

In plain and simple English, you got a "yes."

I would direct anyone who hasn't already seen it to the Verstraeten study (and commentary) at (not I find the comments of Russell Blaylock, M.D. to be particularly enlightening.

And yet--no one is even in jail over this! No one is alarmed!

To go further, when we talk about vaccine safety, we have to go beyond mercury and beyond autism.

We have to take a hard, honest look at vaccine damage since the beginning of mass vaccination. Fortunately, that's not hard to do either, in the sense of "all the information is there," but it is hard to do if you still have a heart and a brain and a conscience and. . .and any moral bearings whatsoever.

Because the history of the vaccine "schedule" shows a history of evil science at its very best: the underlying attitude, sometimes expressed openly, that it is okay to destroy some to save others.

And pushing for a "program," knowing that some will be destroyed, is very, very different from encouraging patients and doctors to use vaccines like any other drug.

If this were done, if vaccines were only used when needed, only to ward off a "likely" threat (not used to ward off "threats" that are mostly theoretical), only used after weighing the potential risks and benefits *to the person about to use the drug,* then the following would no longer be happening:

1.Coercion of parents,
2.Forced vaccination against a parent's wishes,
3.More people harmed by vaccines than saved by them.

I mean--it's one thing to agree to accept a very small risk for a larger benefit (to oneself or one's child); it's another to be asked to play Russian Roulette with your child for "the sake of the greater good."

Most of us think we are choosing the former; we are really choosing the latter.
So while it may seem reasonable to go to our government representatives in hopes of spurring them to action--and while I genuinely believe that this will do some good--we're up against this brainwashing--very deeply embedded into the very fabric of our society--that it is okay if some children suffer and die from their vaccines, as long as other children are saved from even the tiniest, most remote risk of death from natural disease.

When we present a statistic that 1 in 150 children have autism, or 1 in 67, or even when we ask "is there a certain small subset of the population that is particularly at risk for vaccine injury that might lead to autism and other problems?"--we are not only *vastly* understating the damage being done, but we're at risk of seeing yawns and glazed expressions mixed in with the more hardened looks of those already "in the know"--yes, a "tiny percentage" of children will be harmed, but we've known that for a long, long time. Ho hum--anything else?

Once the mindset is in place and the denial is so strong that doctors "try not to think about how they got this way" (as one doctor publicly put it)--it really doesn't matter to most people if it's 1 in 1,000 or 1 in 100 or 1 in 50, so long as (magic thinking, drumroll, please) "it doesn't happen/didn't happen to me or mine."

The best we can hope for, I think, is to stop grossly understating our own position.
Stop downplaying the certainty we now have of the damage, including (but not limited to) autism.

Stop downplaying our certainty and stop downplaying the extent and the types of damage being done--let's go with that 1 in 6 figure we now have of kids with "some kind" of developmental, behavioral or learning disability--seems about right to me, and it seems right if you talk to teachers or others who work with large groups of kids today.

The sickest generation indeed.

If we need to err on the side of being a little too cautious in what we say, or a little too honest, I say let's go for a little too honest.

Because, as Jenny would tell you, it's a frickin' tragedy what we're doing to our own kids.

Terri Lewis


“This is important, of course, because the Verstraeten study was a cornerstone of the 2004 Institute of Medicine report, which found no evidence of a link between thimerosal and autism. It remains a pillar of medical opinion to this day, despite a letter from Verstraeten himself, published in Pediatrics, insisting that his study found no evidence AGAINST an association, and was in fact a neutral study, and that indeed, more research was recommended.”

David, just as Julie Gerberding inadvertently admitted that the VSD study fails to show vaccines safe, Dr. Verstraeten inadvertently admitted that the VSD analysis “shows evidence of a link” that vaccines increase the risk of brain injury and autism. Look again at his letter (PEDIATRICS Vol. 113 No. 4 April 2004, pp. 932). See

“The CDC screening study of thimerosal-containing vaccines was perceived at first as a positive study that found an association between thimerosal and some neurodevelopmental outcomes.”

He then states that since a second study on a different group of children didn’t show the same results - then the totality of the two studies on different sets of children is neutral. But this is not neutral. If ½ of the study for one set of children shows a risk of autism and the other ½ of the study for another set of children is unable to find a risk - then ½ plus zero equals ½, not zero, not null, and certainly not “neutral.” This is evidence of a link. It can not just be dismissed and not mentioned. The IOM and CDC did not show scientific integrity when the two different results were not addressed.

Richard Feynman addressed scientific integrity in his commencement address at Caltech in 1974:

"In summary, the idea is to try to give all of the information to help others to judge the value of your contribution; not just the information that leads to judgment in one particular direction or another."

Likewise in public policy, the CDC, AAP, and FDA should “give all of the information.” Instead they convey the “implication” that vaccines are safe. The question of “is it safe” has NOT been answered. And even Dr. Verstraeten says in his letter “more study is required.”

In Dr. Verstaeten’s February 29, 2000 report and the Simpsonwood/CDC meeting transcript of June 7 and 8, 2000, he repeatedly expresses his concerns about the data trends that he saw – higher mercury levels from vaccines indicated a higher risk of brain injury and autism in children.

This along with the well documented Minamata mercury poisoning disaster is a strong clue to our scientists and policy makers to take all mercury out of vaccines. The USEPA took it out of latex paint in 1990.

And by way David, your critical thinking and integrity should be their role model.

I believe the same issues pertain to the Andrews study 'Thimerosal Exposure in Infants and Developmental Disorders: A Retrospective Cohort Study in the United Kingdom Does Not Support a Causal Association', which was also included in the Institute of Medicine report:

I reviewed this study exhaustively in Red Flags in 2006:

Although there were innumerable anomalies in this study underlying it was the fundamental problem that if you were really trying to detect an effect you would not go to such a weak database (in this case the UK General Practitioners Research Database). In this instance it is particularly interesting to note that after the project, funded by the WHO, was announced it was reviewed by the CDC. Amongst the FOI material which was passed to me was an email of Thomas Verstraeten to Bob Chen:


"I think two issues are important in assessing the potential strength of GPRD study.

"1. Maximum exposure and 2. Unbiased controls

"The maximum exposure is indeed relatively low if that was the only (Thimerosal) containing vaccine used. My estimate is that you need at least >50 (micrograms of mercury) by 3 months or >100 by six months to see an effect if there is one which you can barely make (50 at 3 months and 75 at 4 month in the UK).

"The quality of the comparison group is maybe even more important if you consider all the criticism we have received comparing high Thimerosal exposure to no or low Thimerosal exposure. I am not sure that the GPRD is that reliable that you can be sure low exposure is really low exposure and not underascertainment in the database.

"I hate to say this, but given these concerns, it may not be worth doing this after all. On the other hand maybe the grant can be given to Harald in Sweden todo his follow-up of the DTaP trial kids.."

June 29, 2001 (edited to elucidate shorthand)

Despite these well founded reservations the study was given the green light within a few days. Of course, it was never public that this study, which was commissioned by the WHO and carried out by the UK Public Health Service Laboratory (later the Health Protection Agency) was actually controlled from the CDC.

For those that want a good primer on the flaws inherent in ecological studies you can read this short paper.

It goes over some of the basic issues of the "ecological fallacy" and describes how a regression plot is made to determine correlation. Of course, one could just look at time vs autism incidence like Madsen in Denmark and call it an ecological study, confounding variables be damned.

A retrospective cohort study should be better, but only if the study is designed to identify and segment small subgroups. Checking 1% of the charts of kids in the study did not help matters much. But if one wants to find nothing...

Still, all the genetic research going on now will eventually allow for epidemiological studies on the individual level based on genetic variables, which is apparently what all the members of "Science" are waiting for. That or they just want to abort babies with "flaws" and forget about doing any hard work.


Thank you so much for explaining this. I've had a lot of questions since your original article on the Huffington Post.

It's really good to have a clearer perspective and background on this.


As one who transcribed the Sept. 24 capitol briefings by David Kirby and Mark Blaxill, I can attest that 25 minutes was not long enough to elaborate on most aspects of vaccine-induced autism. One need only ask any advocate who's studied this issue -- for many, since 1999 or earlier.

The comment in question could easily be clarified afterward, so it saddens me that the staff person found defending the bureaucracy more important than asking about victims and affected families.

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