(Managing Editor's Note: We are running the report in three installments this week. The report is available in in full .pdf (Vaccines and Autism Epidemiology HERE)
“We have 16 studies already that clearly state that vaccines do not cause autism.”
-- Amy Pisani, Executive Director, Every Child By Two
“16 studies have shown no causal association between vaccines and autism, and these studies carry weight in the scientific industry.”
-- Dr. Nancy Snyderman, NBC Today Show Medical Editor
“The science is largely complete. Ten epidemiological studies have shown MMR vaccine doesn’t cause autism; six have shown thimerosal doesn’t cause autism.”
-- Dr. Paul Offit, “Autism’s False Prophets”
A NOTE FROM SAFEMINDS:
There are 16 epidemiological studies here on MMR vaccines, thimerosal and autism. These studies represent the most often cited papers by scientists, public health officials and members of the media when trying to refute any evidence of an association between vaccinations and autism.
There are serious methodological limitations, design flaws, conflicts of interest or other problems related to each of these 16 studies. These flaws have been pointed out by government officials, other researchers, medical review panels and even the authors of the studies themselves. Taken together, the limitations of these studies make it impossible to conclude that thimerosal and MMR vaccines are not associated with autism.
SafeMinds would like to acknowledge the previous work in this regard gathered by the "Fourteen Studies project at Generation Rescue.
One additional study on autism and thimerosal was published in September 2010 while this paper was in completed draft form. This study’s methods produced a result that demonstrated that thimerosal exposure was protective against autism. Further analysis of this study is forthcoming but not included here.
MAJOR GAPS IN KNOWLEDGE
Conventional wisdom holds that the autism-vaccine question has been “asked and answered,” and that at least 16 large, epidemiological studies have thoroughly addressed and debunked any hypothesis that childhood vaccination is associated with an increased risk of autism spectrum disorder.
But there are numerous critical flaws in such an oversimplified generalization, and they are rarely given close examination by public health experts or members of the media.
It is particularly discouraging that members of the scientific community are so willing to dismiss a hypothesis that has yet to be fully tested. Overconfident pronouncements such as those found in the quotes above do nothing to advance either the cause of science or our understanding of the complex issues involved. They are, instead, the product of misunderstanding and wishful thinking, brought about by the overzealous drive to ‘disprove’ an unpopular and possibly disquieting theory.
Respected medical opinion-makers such as Dr. Snyderman and Dr. Offit mislead the public when they categorically state that there is “no link” between vaccines and autism. Their misguided conclusions are based on incomplete knowledge and misinterpretations, and likely to be influenced by personal and professional conflicts of interest; conflicts illustrated by their intimate and lucrative financial bonds with GlaxoSmithKline (Snyderman) and Merck (Offit), - two of the world’s leading vaccine manufacturers.
There is a host of reasons why the cavalier dismissal, by scientists and physicians, of any possible vaccine-autism association is premature, shortsighted, and wrong.
But first, some clarification about terminology. Frequently, a counter-claim to those made by the likes of Snyderman and Offit is that ‘epidemiological’ studies cannot be used to establish or refute, causality.
Epidemiology is the study of the distribution and determinants of disease in the human population; the basic science and fundamental practice of public health (Nordness, 2006).
Epidemiological studies may be descriptive or analytical (see for example Hennekens and Buring, 1987), Descriptive epidemiology aims to describe the general characteristics of disease distribution in relation to person, place and time. Studies of this type provide information to health care providers and those responsible for resource allocation and may also be used to generate hypotheses about disease causality, but their design precludes them from being used to test hypotheses.
The studies cited in support of ‘no vaccine-autism association’ are not flawed because they are epidemiological, they are, almost invariably, flawed because their aims, design, analytic procedures or conclusions have been inappropriate, and in some instances, plain wrong.
Analytical epidemiology involves using comparative studies to test hypotheses about associations between an exposure and a disease. Analytical studies can be observational or experimental, but both involve evaluation of associations between exposure and diseases, and both are well placed to do just that.
The studies frequently referred to as indicating ‘no association between vaccines and autism’ have, for the most part, been population-based, observational studies. As such it is quite possible for them to have helped confirm or refute the role of vaccines in causality. The reason they have failed is not because epidemiology is a ‘blunt tool’, nor is it because ‘epidemiology could never pick up on such a small effect’. It is because the studies have either been badly designed, or not designed with the right hypothesis in mind.
In the following analysis, we review and critique the analytical epidemiology studies most commonly cited as evidence against the “autism-vaccine” hypothesis. We must make clear at the outset, however, that this critique addresses only a fraction of the “autism-vaccine” connection. In fact, the studies reviewed here have explored only two discrete (and frequently confused) exposures: one vaccine, the measles-mumps-rubella vaccine (MMR) and one vaccine ingredient, the ethyl mercury based preservative, thimerosal. None of these studies have addressed possible interactions between the two exposures or the effect of these exposures in the larger context of an expanded childhood immunization program. No study has yet been conducted comparing total health outcomes in vaccinated human children with unvaccinated children. As a result, the gap between the study sample reviewed here and a full examination of vaccination exposure and autism risk is remains quite large and largely unexamined.
However, with respect the body of analytical epidemiology on MMR and thimerosal, we draw the following conclusion. The evidence in the studies that are most often claimed to provide conclusive proof dismissing a connection between these exposure and autism do not stand up to close scrutiny. Many of them do not provide evidence one way or another with respect to the hypothesis; some of them provide evidence actually supporting an exposure effect; others are too poorly designed to extract any reasonable conclusions; and in some instance the data have been manipulated in ways that border on misconduct.
In short, although the question of the connection between autism and vaccines has been asked, we have yet to see any reliable and informative answers.
Part 2 to follow.