One of the limitations constraining those of us who do human subjects research is that ethical considerations often prevent us from designing our clinical trials in what would be, from a strictly scientific standpoint, in the most methodologically rigorous way. For example, we can’t intentionally infect human beings with known inocula of deadly bacteria in order to cause a reproducible severity of disease to be treated with a new antibiotic.
One thing that antivaccinationists seem unable to understand is this very point with respect to vaccine trials. They will call for a “vaxed versus unvaxed” study in which children are randomized to receive the full vaccine schedule or saline placebo. Of course, such a design would be highly unethical because the placebo control group would be left unprotected from potentially deadly vaccine-preventable diseases, which violates the all-important principle of clinical equipoise, which mandates that there be genuine scientific uncertainty over which group is receiving the more efficacious and/or safer treatment. Obviously, leaving half of the children in a “vaxed-unvaxed” study would grossly violate that principle. Heck, even from the warped viewpoint of an antivaccinationist, such a trial would violate clinical equipoise, because an antivaccinationist would believe it was the vaccinated group that would be receiving the harmful interventions. Some of the less clueless antivaccine activists have enough understanding of this concept to grudgingly accept that a randomized trial of this sort is totally unethical and therefore cannot be done. As a result they’ll call for an epidemiological study of vaccinated versus unvaccinated children, not realizing that such a study is methodologically far more complex than it sounds, would be enormously expensive, and would likely require nearly as many unvaccinated children as there are in the United States. Such a study would require compelling evidence to justify it, and, as we all know, the evidence that vaccines cause autism, asthma, GI issues, neurodevelopmental disorders, sudden infant death syndrome, or the other problems antivaccinationists blame them for is at best not compelling and at worst nonexistent.
One way to try to get answers when you can’t use humans is to use animals. However, this approach has problems as well, because, depending on the animal model and the disease, the relevance of such experiments can be questioned. One way to try to maximize the relevance to human physiology is to use nonhuman primates, but such experiments are incredibly expensive to do and must be held to very high ethical standards given how human-like they are. I mention these considerations for two reasons. First, one of the most infamous experiments trying to prove that vaccines cause autism—and failed, of course—using Rhesus Macaque monkeys. It was an experiment done by Laura Hewitson, who was at the University of Pittsburgh at the time. Ever since then, periodically, investigators have done experiments with nonhuman primates looking for neurodevelopmental disorders due to vaccines. For instance, Laura Hewitson followed up her first study with another one in 2009 and yet another in 2010. All were bad science. All were preliminary studies at best. All claimed to relate the pediatric vaccine schedule to neurodevelopmental disorders. All were touted by antivaccinationists. One was withdrawn.
Finally, the other day, a good monkey study was released by Gadad et al in PNAS entitled Administration of thimerosal-containing vaccines to infant rhesus macaques does not result in autism-like behavior or neuropathology. Even stranger, Laura Hewitson is one of the authors. Unfortunately, part of the justification for the study were the previous monkey studies that purported to show a link between vaccines and neurodevelopmental disorders. Indeed, so bad were those previous studies that personally I consider this study to be highly unethical to have done, given that there is no compelling evidence to justify subjecting 79 macaque monkeys to a bunch of injections and killing a large fraction of them to study their brains, all in the service of testing the long discredited hypothesis that vaccines cause autism or other neurodevelopmental disorders. I mean, seriously. The University of Washington IACUC, which approved this study, should be ashamed of itself. Ethically, the study is a travesty. It was also a waste of a lot of money, again, because this question did not need to be studied yet again. Despite the lack of a compelling scientific rationale for the study, it was nonetheless done, and done competently; so we have to consider its results which—surprise! surprise!—were completely negative. Let’s take a look at the details.
The design was quite simple. There were 79 infant macaque monkeys subjected to six different vaccination schedules: (i) Control (n = 16), in which animals received saline injections in place of vaccines; (ii) 1990s Pediatric schedule (n = 12), in which animals received vaccines following the pediatric schedule recommended in the 1990s; (iii) 1990s Primate (n = 12), in which animals received vaccines recommended in the 1990s but on an accelerated schedule; (iv) thimerosal-containing vaccines (TCV, n = 12), in which animals received all TCVs but no MMR vaccines following the accelerated schedule; (v) MMR (n = 15), in which animals only received the MMR vaccine but no TCVs following the accelerated schedule; and (vi) 2008 (n = 12), in which animals received vaccines recommended in 2008 but on an accelerated schedule. Infants were assigned to a peer group of four animals, with multiple study groups being tested each year for neurodevelopmental outcomes.
The investigators then assessed social behavior, with testing being carried out by a social tester blinded to the experimental group. The testers were well-trained and experienced; they were also tested for reliability and used standard testing methods:
Infants underwent testing as follows: from birth to 20 d, infants were assessed for the development of neonatal reflexes and perceptual and motor skills; from postnatal day 14 to ∼3.5 mo of age, infants were examined for the development of OCP; from ∼3 to 6 mo of age, animals underwent discrimination learning assessments; from ∼5 to 8 mo of age, animals were assessed for learning set development; and from 30 d to 12 mo of age, animals underwent assessments of behavior before group living. These developmentally appropriate tests are measures of neurodevelopment, learning, cognitive abilities, and social behavior in young macaques (45). At ∼13 mo of age, animals were transferred to juvenile caging where they were group housed (n = 4 males per group) with animals from within their peer group for the duration of the study. All subsequent behavioral data were collected while animals were in their home cage.
Behaviors were defined as passive, exploring, playing, sex, aggression, withdrawal, fear-disturbed, rock-huddle-stop-clasp (strong clasping/grasping of another monkey without play behavior, or self-clasping with arms, legs, hands, or feet, without locomotion and no active inspection of own or other’s body), and stereotypy (repetitive body movements, with or without locomotion, requiring three or more consecutive, repetitive movements). It might be a cliche, but there were no statistically significant differences detected in any of the behaviors measured in any of the experimental groups.
Then, at the conclusion of the experiment, brains from monkeys in the control (N=12), 1990s (N=12), and 2008 groups (N=8) were sectioned for histological and immunohistological examination. The authors examined the brains for neuropathology in parts of the brain previously shown in humans to have changes in autism: the cerebellum, hippocampus, and amygdala. Try as they might to find differences, Gadad et al failed to find any differences between controls and either of the two vaccinated groups examined. There were no changes in the neurons in these regions. There were no changes in protein levels. Basically, there were no differences from control in the two experimental groups in the volume of the cerebellar hemispheres, the number or density of Purkinje cells in the cerebellum. There was no difference in the size of the Purkinje cells. Western blots (a means of detecting proteins with antibodies) failed to find differences in certain Purkinje-cell associated proteins calbindin, GAD-67, and proteins that are markers for different cell types, such as Iba1 (a microglial marker) and GFAP (astrocyte marker). Again, these were all negative. Gadad et al measured these proteins up, down, right, left, and sideways (so to speak), but failed to find any differences.
Why, you might ask, didn’t Gadad et al examine the brains from the monkeys in the other experimental groups? The authors justify this decision thusly:
The neuroanatomical analyses were first performed in brains from the 1990s Primate and 2008 groups, as animals in these groups received the highest amount of EtHg exposure (1990s Primate) or the most extensive vaccine exposure (2008). Because no neuronal differences were found in either of these vaccine groups compared with the control group, no additional vaccine groups were fully studied.
This is a reasonable compromise. If the groups that received the most extensive thimerosal exposure and the highest vaccine exposure showed no detectable differences in brain structure in regions relevant to autism pathophysiology, then there really isn’t a good reason to kill the rest of the monkeys to look at their brains. Even with that compromise, 36 monkeys paid for this information with their lives (16 control + 12-1990s schedule, and 8-2008 schedule) and brains. Basically, this study’s results are inconsistent with the three main “hypotheses”—after all the disconfirming data calling them “hypotheses” really is doing them too much honor—that thimerosal-containing vaccines, MMR vaccines, or and “too many [vaccines] too soon” cause autism. Each hypothesis is represented by an experimental group. Sadly, 36 monkeys paid for these answers with their lives (16 control + 12-1990s schedule, and 8-2008 schedule) and brains, while the rest received at least unnecessary injections and other interventions.
Indeed, Dr. Paul Offit, after listing all the studies that have failed to find a correlation between vaccines and autism, alluded to a similar same concern in an accompanying editorial, although characteristically he was nowhere near as blunt as I am. Characteristically, he refrained from calling the study unethical and a waste of money and tried to find something good about this waste of money and primates:
One could reasonably wonder whether it is necessary to continue to spend more money chasing this fruitless, dead-end hypothesis. However, the constant drumbeat of negative studies has made a difference. Unlike 10 y ago, the media no longer covers the vaccine– autism controversy by telling both sides of the story when only one side is supported by the science; for the most part, they have chosen perspective over false balance. Legislators are also stepping up; both California and Vermont recently eliminated their philosophical exemptions to vaccination.
I will admit that Dr. Offit has a point. There certainly is a value in negative studies. No one, least of all I, would dispute that. The question—and reasonable scientists can disagree over the answer to this question—is: What is the point where we can say that enough is enough, that the question being studied has settled to a sufficient degree of certainty that it is no longer worth spending large sums of money on or killing intelligent primates to ask and study the question yet again? An animal study like this might be considerably less expensive and complex than large epidemiological studies, but it’s still an animal study. It’s not a human study. Human epidemiological studies, on the other hand, are much more expensive and require controlling for confounders that don’t need to be controlled for in the highly controlled world of animal studies.
Unfortunately, I would argue that the relentless drumbeat of negative studies about vaccines and autism has probably played less of a role in how the press has changed its tune in the way it covers vaccine-autism pseudoscience to a far less credulous one than the discrediting of the chief architect of the MMR-autism scare, Andrew Wakefield, did. As much as I really, really wish it were the science alone that finally turned the tide and persuaded reporters and much of the general public that vaccines do not cause autism, I tend to think that was less of a factor than Wakefield’s disgrace. From my perspective, seeing Wakefield lose his medical license, be dismissed as the medical director of the quack clinic he used to run in Texas, have his Lancet paper that launched the MMR scare retracted, and be shown to have been a scientific fraud practicing what Brian Deer so aptly called “Piltdown medicine” probably played a far greater role in changing public perception. Add to that the string of outbreaks of vaccine-preventable diseases that culminated in the Disneyland measles outbreak early this year. These things, more than anything else, were likely what shifted public opinion. That’s why it’s my opinion that, barring new compelling evidence that demands that we study the question further, studies such as this one are unnecessary.
Particularly annoying to me was the way that the authors of this study basically twisted themselves into pretzels to justify doing the study. For example:
Several epidemiological studies sought to determine whether TCVs resulted in neurodevelopmental disorders including autism; however, both nonsignificant and significant associations have been reported (8–12). Significant associations have been reported by Thompson et al. (11), who investigated the association between TCVs and immune globulins early in life and neuropsychological outcomes in children at 7–10 y of age. The data included the evaluation of 1,047 children and their biological mothers and 24 neuropsychological tests. The only variable that was statistically significant was tics; children who were exposed to higher doses of thimerosal were more likely to exhibit tics. In a follow-up study by Barile et al. (12) examining a subset of the data from Thompson et al. (11), they found a significant association between thimerosal dosage and tics, but only in boys. They found no statistically significant associations between thimerosal exposure from vaccines early in life and six of the seven neuropsychological constructs examined.
William Thompson, as you might recall, is the “CDC whistleblower,” and the above is a total cherry pick job on Thompson’s studies. While Thompson’s 2007 study did show a statistically significant association between thimerosal-containing vaccines and ticks, what Gadad et al totally fail to mention is that the study didn’t correct for multiple comparisons and that it also showed positive associations between thimerosal-containing vaccines and positive outcomes. That’s why the overall conclusion is that the pattern of associations was most consistent with random statistical noise. Funny how Thompson (and Gadad et al) mention the ticks but ignore the seemingly positive associations.
In the abstract, studies like this one do have value—to a point. Given the evidence we have and what we already know about the relationship between vaccines and autism (namely that there isn’t one), however, I really have to question the very necessity for such a study. Sure, it shows what every other well-designed study asking whether vaccines, be they thimerosal-containing or not, are associated with autism, but surely the investigators must have known before they started that that’s what it would show. Worse, I can predict exactly what the antivaccine faithful will say about it. They’ll dismiss it as an animal experiment and continue to call for either an experiment even more unethical than this one (a randomized trial of “vaxed versus unvaxed”) or an epidemiological study of “vaxed versus unvaxed” children that they can dismiss because it’s an epidemiological study prone to all of the confounders that epidemiological studies are prone to.
At least I can hope that after this study no more primates need die in the service of a dead, discredited hypothesis. A bigger challenge will be preventing children from dying because belief in this discredited hypothesis leads parents not to vaccinate their children against deadly diseases.