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June 23, 2005

Simpsonwood, thimerosal, and vaccines (II)

Robert F. Kennedy Jr. claims that the transcript of the CDC's Scientific Review of Vaccine Safety Datalink Information (hereafter, Simpsonwood) is definitive proof of a government/industry conspiracy to conceal the health effects of thimerosal in vaccines.

What follows is a discussion of the CDC/Vaccine Safety Datalink thimerosal study as presented at Simpsonwood retreat center in Norcross, Georgia in June of 2000. An expanded and updated analysis of the CDC/VSD data was published in 2003 in the journal Pediatrics.

The Vaccine Safety Datalink (VSD) was a collaboration between the CDC and major health maintenance organizations (HMO). The CDC acted as a clearinghouse for vaccine-related medical records from four major health maintenance organizations. The VSD received three major kinds of data from the HMOs: automated vaccination records, patient data (gender, birth date, enrollment), and outcome data (hospital discharge diagnoses, coded outpatient diagnoses).

The outcomes of interest to the thimerosal investigators were primarily outpatient diagnoses. Therefore study was restricted to Group Health (GH) and Northern California Kaiser Permanente (NCKP) because these were the only two VSD HMOs with adequate outpatient records.

The goal of the Simpsonwood studies was to see if thimerosal exposure was correlated with virtually any health outcome that has ever been linked to mercury poisoning in the medical literature. Thimerosal exposure was calculated by the number of thimerosal-containing vaccines (TCV) each patient received. The investigators calculated cumulative exposure to thimerosal at 1, 2, 3, and 6 months.

Phase I of the study used the patient records of about 110,000 children. The interval studied was 1992 to 1997. The original screening identified 200,000 infants who had received at least one thimerosal containing vaccine during their first year of life. However, in order to be considered for the analysis, a child had to have been born into the HMO and enrolled continuously for its entire first year of life. As anyone who has ever done a database analysis will tell you, this is not a trivial criterion to meet. Many HMOs have 20% annual turnover.

Subjects were also excluded if they suffered from any major congenital or perinatal disorder (fully 25% of the total potential sample) or prematurity (5%, analyzed separately). The investigators decided to exclude patients who received less than 2 polio vaccines during their first year of life on the grounds that a child who didn't even get those (non-TCV) shots probably just wasn't being taken to the doctor.

After all was said and done, a potential sample of approximately 200,000 had been winnowed to about 110,000.

The following thimerosal-containing vaccines (TCV) were available to the cohort: hepatitis B (HB), diphtheria/pertussis (DPT), acellular DPT, h influenzae B (HiB), and a DPT/HiB combo. The investigators were able to ascertain that all vaccines of interest contained thimerosal (except the aforementioned polio vaccines).

Unfortunately, the kids in the cohort received different vaccines in different combinations at different ages. If thimerosal has any effect, it is a probably a specific and subtle toxicological relationship. Any of the following variables might interact to modify the effects of thimerosal: the age of the patient at exposure, body weight, the specific vaccines administered, the spacing of the doses, etc. Unfortunately, the Simpsonwood experiment simply wasn't capable of disentangling such subtle relationships, if they existed.

The Simpsonwood study is often cited as evidence of a coverup of data supporting the autism/thimerosal hypothesis. In fact, no phase of the study ever found a statistically significant association between autism and vaccine exposure. (At least none of the data discussed at the retreat supported the autism hypothesis, I've heard unconfirmed allegations that the CDC has yet more embargoed analysis pointing to such a link.)

Anyway, here is the money shot from Simpsonwood:

From those risk analyses, excluding the dichotomized EPA, we have found statistically significant relationships between exposure and outcome for these different exposures and outcomes. First, for 2 months of age, an unspecified developmental delay which has its own ICD-9 code. Exposure at 3 months of age, tics. Exposure at 6 months of age, attention deficit disorder. Exposure at 1, 3, and 6 months of age, language and speech disorder, which are two separate ICD-9 codes. Exposure at 1, 3, and 6 months of age, the entire category of neurodevelopmental delays, which includes all of these, plus a number of other disorders.--Thomas Verstraeten, Simpsonwood transcript, p 40-41.

The transcript shows that the assembled experts agree that the data are interesting, and that the effects of thimerosal on neurological development deserve further study. However, they are also acutely aware of the severe limitations of the study, especially as a guide to policy making.

The Simpsonwood study could not have established a causal link between thimerosal and ill health. The study is sophisticated accounting of correlations. The original data show that infants who got more vaccines (or got their vaccines "on time") were also more likely to be diagnosed with certain neurological conditions later in life.

What might this mean? Maybe thimerosal in vaccines caused the problems. The most likely alternative explanation is that conscientious parents who vaccinate their kids on time are also more likely to seek treatment and obtain diagnoses for more subtle neurological symptoms like speech delay and ADHD.

Of course, there are confounds upon confounds. Care-seeking may be related to socioeconomic status, socioeconomic status to maternal mercury intake and breast feeding, and therefore to prenatal and postnatal mercury exposure, and so on. You can generate any number of alternative scenarios.

It is difficult to interpret the Simpsonwood data because the diagnoses of interest are so fuzzy. The study is trying to capture small differences in the relative risk for relatively rare conditions. As we learned from the recent JAMA obesity study, if you're studying a relatively rare phenomenon, like death at age forty (or infantile autism), small numerical differences between groups translate into huge increases in relative risk. Under these circumstances, it's especially important to be mindful of confounds that could account for small differences between the groups, e.g. local variation in diagnosis rates and diagnostic criteria in the case of relatively subtle and fluid diagnoses like "speech delay" or "attention deficit disorder."

As one of the pediatric neurologists at Simpsonwood pointed out , most of the kids in the study were too young to be diagnosed as speech delayed or attention deficit disordered with any degree of rigor. There's just too much overlap between the "normal" and the "pathological" curves at that age. Of course, once someone gets diagnosed with something, it's pretty rare for them to get undiagnosed, especially in the eyes of an administrative database. So, it's unclear how many kids with early diagnoses actually had a pathological problem to begin with.

It is very suspicious that diagnosis rates varied so dramatically between the HMOs for many of the outcomes of interest. The discrepancy was so great the authors had to present the data from each one separately. For example, speech and language delays were diagnosed much more frequently at Group Health (which has a specialized speech and language pathology center) than at Northern California Kaiser. I haven't crunched the numbers, but I bet that enrollment in Group Health posed a larger relative risk of a speech and language delay diagnosis than full vaccination.

The toxicology experts at Simpsonwood were skeptical because the data didn't seem to show a classical dose/response curve. Many also objected that the diagnoses observed weren't plausible results of mercury poisoning. They pointed to epidemiological studies of children exposed to much higher doses of methyl mercury prenatally and in infancy. Critics countered that there is very little toxicological data on ethyl mercury (thimerosal) and that it was unfair to compare acute vaccine-related exposure to daily exposure to chronically high levels of mercury.

The bottom line is that all the Simpsonwood data showed was a correlation between number of vaccinations and subsequent language problems and ADD. These correlations may have been caused by confounding variables (like health-seeking behavior) rather than by any aspect of the vaccination. Even if we suppose that vaccination caused the problem, we still have no particular reason to assume that thimerosal is the harmful substance. As the experts noted, any number of alternative substances or mechanisms might account for the results: aluminum, the vaccine antigens, autoimmune reactions in susceptible patients, etc.

Robert F. Kennedy Jr. argues that the CDC should have immediately banned all thimerosal vaccines on the basis of the Simpsonwood data. That would have been an absurd overreaction. A year before Simpsonwood, federal public health authorities had already committed to removing thimerosal from the vaccine supply, which is worthwhile goal. Thimerosal is, after all, a preventable source of mercury exposure.

However, in 1999 there were no thimerosal-free hepatitis B vaccines suitable for administration at birth, there was a t-free vaccine on the market, but it was only indicated for infants aged 2 months. The CDC policy makers felt it was unacceptable to delay HB vaccination from birth to 2 months because of an unsupported theoretical concern about mercury. Since thousands of US infants are exposed to HB at birth, a delay in vaccination would have resulted in significantly more babies getting hepatitis B.

The anti-vaccine activists are busily mining quotes from the Simpsonwood transcripts. Towards the end of the meeting, Dr. John Clements says that the CDC should never have conducted this research project because the results created a legal and PR nightmare for the agency. Other participants note that these results would be a bonanza for "plaintiffs' attorneys" and "junk scientists" seeking damages. These fears are not entirely unjustified.

Obviously, it's disheartening to hear someone say that PR should dictate a research agenda. However, it is important to interpret this remark in context. Clements was pointing out that this study was an incredibly crude method to investigate a complex, emotionally and legally fraught issue. He is correct that the Simpsonwood study could never have settled the thimerosal issue one way or the other, or even shed much light on the matter. The countervailing argument, which was also repeated frequently at the meeting, was that the CDC had better do this research, not because it was an urgent scientific priority, but because they had to be on the record as having looked into thimerosal (again, for PR reasons).

The critics are making a big deal out of the fact that the information presented at the meeting was "embargoed." If you read the transcript, you see that participants were only sworn to secrecy until ACIP meeting the following week.

Whether the CDC acted properly in this case depends on what its usual level of transparency is for preliminary studies like the one presented at Simpsonwood. Maybe someone who is familiar with the workings of the CDC would like to comment on how the agency usually handles preliminary data of this kind, and whether there were departures from standard operating procedure for the thimerosal data?

RFK's article gave me the impression that Phase II of the study was an ad hoc modification to the original study protocol. However, the original proposal always included a provision for a Phase II study if Phase I generated any interesting results. (Cf. link: VSD Thimerosal Study Background.) Judging by the Pediatrics article, Phase II was conducted as described in the original proposal. The only controversial feature of Phase II was the decision to use an HMO based in Massachusetts as a cross-check on the Phase I results. According to the transcript, the rationale was that Harvard Pilgrim was the only organization that promised to deliver a preliminary analysis in time for the upcoming ACIP policy meeting.

Nothing said at Simpsonwood suggests an attempt to whitewash or cover up anything. The study got some interesting results, which later failed to withstand verification at the third HMO. Vaccine experts said some nasty things about anti-vaccine activists. That was about it.

As yet, a link between thimerosal and autism is just one more unsubstantiated etiological hypothesis. I'm prepared to accept that small doses of injected mercury might have deleterious effects in susceptible infants. Maybe some forms of autism are caused by inborn errors of heavy metal metabolism or autoimmune defects and maybe these conditions are exacerbated by vaccination or vaccine preservatives. However, it is absurd to conclude from the evidence at hand that mercury poisoning is a major cause of autism. If the effect were that big, we'd see decreases in autism corresponding to decreased thimerosal exposure in the developed world. Maybe it's too soon to see results, but more likely the effect (if there is any) is so small as to be obscured by much larger trends.

Erratum: I accidentally published the wrong draft of this post. The earlier version included an incorrect statistic about the percentage of US infants exposed to hepatitis B at birth. I wrote, incorrectly that 10%-15% percent American infants were exposed. The actual number of infants exposed at birth in the US is about 19,000.

The current draft of this post also includes additional commentary.


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» thimerosal update from Big Monkey, Helpy Chalk
So why has only posted a link to the discredited Salon RFK Jr article? Lindsay is doing a better job of covering this issue on her own time than the pros are. [Read More]

» thimerosal update from Big Monkey, Helpy Chalk
So why has only posted a link to the discredited Salon RFK Jr article? Lindsay is doing a better job of covering this issue on her own time than the pros are. [Read More]

» Thimerosal update from Skeptico
I thought I would link and summarize some other bloggers’ posts and other feedback on Robert F. Kennedy Junior’s ridiculous thimerosal scare piece that I commented on unfavorably last Monday. My original thread attracted a lot of comment, and much [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]

» Spurious correlations re: thimerosal vaccines and Sabbath law from Quicksilver כספית: A commentary on rabbinic texts and toxicality
With articles by the New York Times, CNN, and RF Kennedy Jr. [... [Read More]

» Mercury and autism: RFK Jr. drops another stinky one on the blogosphere from Respectful Insolence
I had wanted to let this cup pass, but couldn't, not after several readers e-mailed it to me and I went and experienced its inanity first hand. As Michael Corleone said in The Godfather, Part III: "Just when I thought I was finally out, they drag me ba... [Read More]


Totally off-topic, but I can walk to Simpsonwood from my house. I would hardly call it "wooded farmland"
On topic, my 21-year old sister is autistic. My mother clings to the belief that vaccines made her that way. When someone can't tell you why something happens, people tend to attribute it themselves. Maybe if my parents were more religious, they'd say God did it. Parents of autistic children tend to be a little more aware of the scientific world however. They still need a scapegoat. My wife is scared about vaccinating our future kids and is scared of a potential genetic link. Neither one is supported by science. Unless we find some real causes for autism, all the debunking in the world won't set peoples' minds to rest.

Knocked another one out of the park, Lindsay. I only wish your careful analysis had some hope of gaining as much media attention as the Salon/RS hit piece is sure to get.

What is difficult about this question is that the incidence of autism begins at the same time that children are undergoing vaccination.

When breast implants were blamed for autoimmune diseases (another class of diseases with a causation question mark), what was hard for many victims to understand was that the incidence of autoimmune diseases especially in women rises every year from age 25 to 45 -- approximately the same age range when women were likely to seek breast implants. So it's easy to believe the link exists.

Indeed, some link vaccine to neurological incidents regardless of the preservatives used in the vaccine. And I am shocked and would like to see the evidence that 10-15% of babies are at risk of exposure to Hepatitis B -- Surely, there are ways of determining who those babies are without overloading infants who are not at such high risk.

This is what bugs me about the CDC -- the inflexible belief that these vaccines must be delivered at infancy because of theoretical exposure risks that don't seem real. My suspicion is that in reality, they want them delivered during infancy because that's when mom is most likely to show up for them. It raises the compliance rate overall, until such time as the kid is school age, and then has to have them to enroll.

Still, talk science all you want and then ask yourself: does mercury need to be in vaccines? And if not why should it be? Of all the medical products in the world, it seems to me that we should be the most risk averse about the constituent parts of a vaccine that is intended to be (and is often required to be) universally administered to the most vulnerable of patients.

Well presented Lindsay.

It is curious to me that there are two very large spikes in the population base that are neurological disorders. The first is autism and the second are the neurodegenerative disorders (Parkinon's, ALS, MS).

In the case of the later one, the CDC and NIH put out a warning that anyone over the age of 40 should be taking a sublingual B-12 supplement because 70% of the population have Atrophic Gastritis and can't absorb B-12 through the gut. B-12 being essential for cognitive functions.

They didn't say that it was a causal relationship, but the one factor that all of the neurodegenerative disorders have is B-12 deficiency.

It is two different age groups and probably not related at all, but its curious none the less and both have caught the attention of CDC and NIH.


The vaccine is given at birth for both reasons: to protect babies from HBV exposure at birth (20,000 infants a year are at risk of HBV from HBV+ moms, many of whom do not know their status as such), and to acculturate the parents toward getting the appropriate vaccines on time. The CDC has not hidden the latter as a policy goal. See this CDC memo, for example (pdf file), in which the ACIP states its support for the birth dose because: "3. Initiating the hepatitis B vaccine series at birth has been shown to increase a child's likelihood of
completing the vaccine series according to the recommended childhood schedule."

Jack, I find that problematic. I understand as well as anybody the public health imperatives at work here, and the basic "everybody is stupid and noncompliant" supposition that must go into certain types of public health measures. But the CDC is not entitled to treat everyone like children to the point of understating every kind of risk. Lack of transparency and conflict of interest are going to kill its efforts if even people like me no longer trust it.

And I would happily take an HBV test in order to determine the risk profile of my baby if it lessens other types of risk to him. Indeed, it's such a good idea I think I will tell this to my pediatrician when the time comes.

Sorry, everyone. I accidentally published the wrong draft of the thimerosal II post. The correct version is up now.

Thanks for catching the HB statistic, Barbara.

It occurs to me that if we had a single-payer healthcare system, patient histories would be more amenable to useful statistical analysis. It is of no use now, for this issue, but I'm sure we'll be asking, "What is causing the increase in _______?" 50 years from now.


You would need to elaborate upon your use of "understating" before I could adequately respond to that remark: For example: what about the mandatory vaccine information statements given out at vaccine delivery are "understated"? Given the myriad solid, large, peer-reviewed studies which have not found significant evidence that thimerosal causes autism, are you implying an "evolution is one of many theories"-type side effects warning be included on the handouts?

And your use of "inflexibility"/"lack of transparency"/"conflict of interest" belies a position that there has been some sort of conspiracy undertaken here.

Jack, re your points:

Transparency -- no waiver I ever signed explained that vaccines are given early in infancy because the CDC is worried about low compliance and thinks most mothers are sufficiently indifferent to their children's health that they won't follow through. In fact, to be honest, no explanation at all is ever given as to why a vaccine is given at a specific time.

Inflexibility -- Vaccines are hardly presented as an option. I had a premature baby and the pediatrician was insistent that they be given on schedule. Risks are pooh poohed.

Conflict -- Those that advise the CDC have significant financial relationships with vaccine makers regarding the marketing of vaccines. I don't think this should ever be permitted, and I mean never. This alone causes me to rethink the safety of vaccines. It taints the whole process and raises serious doubts about the integrity of the agency's decisions.

Believe me, I had my kids vaccinated on schedule, but it was news to me that vaccines had mercury in them. Whether you like it or not, compliance of large numbers of people like me doesn't depend on whether science that we barely understand is valid (I probably understand it better than most), it depends on the degree of trustworthiness of the agency and the degree to which we believe that it makes its decisions based on science, and yes, whether it is cautious and conservative in assessing risks or whether it is arbitrary or trying to advance an altogether different agenda -- such as the viability of vaccine makers. The latter is necessary, but if it is perceived to be too important of a goal, then people will be justified in believing that the agency considers something other than their children's best interests to be more important and act accordingly.

So it is not merely "unfortunate" that CDC staff made comments about PR, etc. It was stupid and damaging. And you can't expect any other reaction when it comes to the way people look at the health of their children. It may be totally irrational, but hey, why should the CDC presume that we are all rational for purposes of this exercise when it doesn't grant us the same presumption when it comes to devising the optimal schedule for giving vaccines?

terrific. thanks so much for the hard work.

Taking your points one by one:

Regarding transparency: how often are policy decisions written on any prescription/drug insert? As for the timing of the vaccines/explanation: multiple doses to ensure the highest likelihood that immunity has been achieved, and early in life to ensure that these children do not become vectors for deadly/dangerous infectious diseases when they are both most vulnerable and most likely to be in a situation where they can transmit such illnesses (daycares and early school years).

Inflexibility: vaccines are not, nor should they be treated, the same way as, say, you deciding whether or not you want to take a drug for high blood pressure. The infectious disease risks means that your decision on whether or not to vaccinate can have ramifications for your child, your family, and those with whom your child and family come in contact. That's not to say there are no "options" when it comes to vaccines. Parents opt out all the time. However, there are ramifications for doing so, such as possible restrictions on participating in certain activities or opportunities. The pediatrician you describe sounds pretty flippant with your concerns, if you expressed them at the time. I hope you changed pediatricians if you felt this represented their level of caring for your child. I know many pediatricians who would be far more explicit with their discussions on such matters.

Conflict: All people involved in this debate have "conflicts," as has been pointed out in numerous links Lindsay has provided. Insofar as the vaccine schedule is concerned: There are multiple checks and balances within the system. The FDA needs to approve the vaccine for use. The CDC recommends, they do not mandate, immunization schedules for children, adolescents and adults. The states ultimately decide what vaccines will be recommended or required for their populations, and school systems (usually) determine how such vaccine requirements will be enforced. How does that compare with, say, Andrew Wakefield?

I understand that public health measures rely on trust. And that is why I am gravely concerned when such a one-sided slam piece like the one Kennedy published ends up framing the discussion, because the people who are at the CDC working on infectious disease control are not trying to poison your children or cover for the vaccine makers. They are trying to make the best recommendations and policy decisions possible with the best information and evidence available at the time they make it, and they scrupulously monitor those determinations and make dramatic changes when necessary and/or viable (as was the case with recommending to pull thimerosal from the childhood vaccines in the first place).

The discussion of PR is a very real issue in the health care world, unfortunately, and is especially challenging in public health. That's because much of public health's achievements are essentially silent -- politicians don't often stand up and crow that we saw a 1.5% reduction in some health statistic over 5 years -- whereas any "failures" of public health are very public and very damaging. Furthermore, because public health is very much a government-based enterprise, its link to politics is unseverable. Would that there were a better way to provide and fund community-oriented health measures.

Jack, the FDA has had quite a few misses over the last several years. (Vioxx or Rezulin anyone?) The CDC is catching up fast. Like I said above, science is not the determinant here. Trust is. If an agency takes the position that inflexibility and lack of discretion on the part of the consumer is paramount to achieving its goals it had best be lily white when it swings its hammer and yells "thou shalt". I should say that I work on the periphery of this world and the notion that checks and balances are in place to save us from bad decisions is, at best, naive, and more likely laughable if the consequences weren't so potentially grim. It isn't so, and this is not a conspiracy theory on my part. The industry simply has too much sway over what is approved and how risks are presented and more often than not downplayed.

And to say that because everyone has conflicts no one can complaint that the very people responsible for assessing the evidence also have conflicts is just silly. They are the ones who are accountable to the public, not the naysayers on the sidelines. If they don't like it that way, they should quit.


Again, I agree that trust is a large determinant of successful public health measures; however, we must agree to disagree on much of the rest of the discussion.

I do not believe our government or our public health agencies are infallible or immune from influence. I also believe they should be rigorously and fairly questioned.

In the context of childhood immunizations, I do believe, based on my long personal involvement in these areas, that issues concerning safety are scrupulously being examined before, during and after the approval process. To me, the fact that there was a Simpsonwood study and conference involving all of those major players from around the world supports the dedication to ensuring accuracy and safety, in contrast with Kennedy and his cloak-and-dagger characterizations. I also believe that individual rights and the protection of the public's health are fairly being balanced.

And my point about complaining about conflicts was not that no one should complain. However, those raising accusations who themselves have conflicts should have their conflicts examined to determine whether their argument may have been influenced by such relationships. We do it to Tom DeLay and Fox News, for example. That is by no means what Kennedy did in his piece.

When my grandson was born 5 years ago, my daughter was deeply concerned about this issue. Now, I am not a scientist, but I am a more-than-ordinary lay person, having edited medical books for more than 30 years. Moreover, my husband is a survivor of the very last polio epidemic before the vaccines were available.

As a very concerned grandmother, and because we live not far from the Mexican border in Arizona, I put the quandry to her this way: We know what polio does, immediately and 50 years post (my husband now uses a wheelchair, but his used crutches for 40 years, and he is getting weaker with post-polio syndrome). Both my kids had their vaccines on time. They are bright and healthy in their late 20s. Today populations--both rich and poor--move quickly and from very far places. Was she willing to allow her child to risk possibly devastating infections from such spare suspicions (in a climate of political intrigue, globalization, mounting poverty, etc. etc. etc.) One can posit conspiracy theories and greed theories, and yes, some might be true, but in this case the risk DOES NOT COME CLOSE to the benefit.

Think of the third-world populations deprived of AIDS treatment because "it is a white-man's plot." or the developed world women deprived of reproductive control because it is "sinful." We have so many things coming down on us that we need to be smart. Give the benefit of the doubt to those aspects of modern medicine that have proved beneficial for 45 years!!

For me, this is a no-brainer.

When my grandson was born 5 years ago, my daughter was deeply concerned about this issue. Now, I am not a scientist, but I am a more-than-ordinary lay person, having edited medical books for more than 30 years. Moreover, my husband is a survivor of the very last polio epidemic before the vaccines were available.

As a very concerned grandmother, and because we live not far from the Mexican border in Arizona, I put the quandry to her this way: We know what polio does, immediately and 50 years post (my husband now uses a wheelchair, but his used crutches for 40 years, and he is getting weaker with post-polio syndrome). Both my kids had their vaccines on time. They are bright and healthy in their late 20s. Today populations--both rich and poor--move quickly and from very far places. Was she willing to allow her child to risk possibly devastating infections from such spare suspicions (in a climate of political intrigue, globalization, mounting poverty, etc. etc. etc.) One can posit conspiracy theories and greed theories, and yes, some might be true, but in this case the risk DOES NOT COME CLOSE to the benefit.

Think of the third-world populations deprived of AIDS treatment because "it is a white-man's plot." or the developed world women deprived of reproductive control because it is "sinful." We have so many things coming down on us that we need to be smart. Give the benefit of the doubt to those aspects of modern medicine that have proved beneficial for 45 years!!

For me, this is a no-brainer.

Dorothy, it should be a no-brainer. The fact that so many believe that it is not should keep the CDC up at night wondering about its methods and its ability to communicate public health risks.

I am not positing a conspiracy. I am positing a culture that is too often willing to defer hard questions based on entrenched assumptions such as, for instance, vaccines are always good, as well as a culture that has a lot of difficulty admitting the importance of secondary considerations -- such as, rewarding vaccine makers for staying in the industry.

My second daughter was required to have a chicken pox vaccine, for instance, and it still makes me angry because of the likelihood that she will get the disease as an adult instead. It is, for most children, a much milder experience.

You also probably don't realize that the vaccine schedule that today's children undergo is much heavier than the one your children underwent. Certainly it is much more intensive than the ones I was required to get -- which was, basically, polio. I did not have MMR, I did not have HIB, HB, chicken pox. I might have had DPT (in whatever form it came in) at the time, but I don't think so. I did have a small pox vaccine (which is no longer given).

Look at the HB vaccine, for instance: Approximately less than 1 percent of children are exposed to HB through their mothers. Here is what a medical site says about HB:

"Although relatively rare in the United States, hepatitis B is endemic in parts of Asia where hundreds of millions of individuals may be infected. HBV is transmitted horizontally by blood and blood products and sexual transmission. It is also transmitted vertically from mother to infant in the perinatal period which is a major mode of transmission in regions where hepatitis B is endemic."

Please explain why 100% of American children should be vaccinated against HB in the first six months of life.

Nicely done summary. ER had an episode where a kid dies of measles, which allowed the writers to preach about the dangers of not vaccinating. I wonder if someone could provide the estimated incidence of autism per 100,000 births, or the estimated number of cases that develop in the country each year, or something equally understandable, followed by the worst case scenario for additional ethyl-mercury induced cases. I have no feel for whether there are 1000 new cases each year or 50,000. I used to use methyl mercury in the lab (it is an effective RNA denaturing agent, which is important in getting good molecular weight determinations etc) and we were very careful to use fume hoods. We also read the literature on Minamato Syndrome, which was caused by ingestion of methyl mercury polluted fish (due to pulp mill pollution). The amounts of the stuff that was routinely ingested was staggering, and it chewed up great holes in the brain.

The dangers of not vaccinating for measles and polio are one thing. Measles is especially problematic because many recent immigrants have neither immunity nor vaccine. Polio is probably less of a wild card, but its threat definitely continues globally and could easily recur in the U.S. However, the dangers of not vaccinating for HIB, HB, and Varicella (chicken pox) are another. HB is very difficult to transmit, and rare in the U.S. Varicella is generally milder in children than in adults. And there is a question about the continued viability of either of these vaccines into adulthood, especially an issue for HB. HIB probably depends on whether a child is in daycare -- if so, it's a good idea.

Yet, all of these vaccines are equally mandatory for school children (and more importantly, for daycare -- when children are younger). And they are all presented as if there are profound risks associated with rejecting any of them. This is what I mean by inflexibility and trading on fear and ignorance in order to promote an unthinking "vaccine good" policy. HB is especially outrageous, as it is given at birth and probably won't even continue into the period of time when an individual might actually be at highest risk.

Just a thought real quickly on studying this... has anyone attempted to look at autism rates amongst religions that don't allow modern medicine? Wouldn't that be a somewhat good way to further analyze the issue-- by looking at Christian Scientists, Jehova's Witnesses, the Ahmish etc.?

Although I don't have sources, there was a study done regarding the Amish that is cited by thimerosol opponents in support of a link.

FYI I did speak with my pediatrician who said that she thought Varicella and HB vaccines are not nearly as important as the others (DPT/Polio/MMR). I don't think I'm smoking something to feel that the CDC is inflexible in its adherence to such an aggressive vaccine schedule for infants. All interventions, including vaccines, have potential side effects, whether autism is one of them or not. Forcing an intervention should have a compelling, not merely an "because it's a good idea" justification.

As A parent of an Autistic child I wish that all of the people out there who DO NOT have to live with this on a daily basis would use your enegy an "great" wisdom to get out there and do somthing to help these children. Raise money or just awareness about this horrible affliction, volunteer at a program who cares for these kids, anything but please STOP supporting the people who DO NOT give a care about these kids but are only interested in making money an covering there own asses with it.

As a father of two children with autistic symptoms, I echo Marc's exhortation to people to help these children. I would further exhort parents of these kids to abstain from false notions, like the thimerasol bunk, and just focus on assisting your child to reach his fullest measure of independence and happiness. Letting our anger get the better of us serves nobody, and villifying the all too human pharmaceutical companies takes our attention away from what should be its focus, teaching our children.

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