The CDC has changed the title of their webpage giving information about vaccines and autism from “Vaccines Do Not Cause Autism” to simply “Autism and Vaccines”.
Why did they change it? It could be due to the legal action of ICAN, or it could be an innocent “reformatting” of the website, as CDC defenders are claiming.
As both sides acknowledge, the text of the page is unchanged and still says that “vaccines do not cause ASD”, and that “there is no link between receiving vaccines and developing ASD” and “no links have been found between any vaccine ingredients and ASD”.
ICAN intend to pressure the CDC to remove these statements, too, because they say they are not supported by the scientific evidence.
Let us assess whether ICAN are right by looking at each of the sources cited by the CDC on this page to support their claim that vaccines do not cause autism.
Institute of Medicine, 2012
Under the heading “There is no link between vaccines and autism”, the CDC writes that:
Some people have had concerns that ASD might be linked to the vaccines children receive, but studies have shown that there is no link between receiving vaccines and developing ASD. In 2011, an Institute of Medicine (IOM) report on eight vaccines given to children and adults found that with rare exceptions, these vaccines are very safe.
That Institute of Medicine (IOM) report was called “Adverse Effects of Vaccines: Evidence and Causality” (2012) and is a systematic review of all the scientific literature looking adverse effects of vaccines. The eight vaccines included in the study were MMR, Varicella, Influenza, Hepatitis A, Hepatitis B, HPV, DTaP, and Meningococcal. An impressive 76 different health outcomes were included in the study, one of which was autism.
However, only two vaccines – MMR and DTaP – were even examined in relation to the autism health outcome. Presumably, this is because there are no studies to examine. This alone makes the report insufficient evidence to claim that vaccines don’t cause autism. For all but two vaccines, according to the IOM, there have been no studies looking at associations to autism.
Regarding DTaP, the IOM concluded that:
The evidence is inadequate to accept or reject a causal relationship between DTaP and autism.
Their epidemiological assessment found the evidence “insufficient” (just one single study, rejected due to being based on data from a passive reporting system). Their mechanistic assessment found the evidence “lacking” (no studies at all).
The MMR is the only vaccine where the IOM made a conclusive statement:
The evidence favors rejection of a causal relationship between MMR and autism.
At best, therefore, this report supports the claim that the MMR does not cause autism. It cannot possibly support the bigger claim that vaccines do not cause autism.
MMR-Autism Studies
In their epidemiological assessment, the IOM reviewed an impressive 22 studies looking for an association between MMR and autism. 12 of them were dismissed for being based on data from a passive surveillance system lacking an unvaccinated comparison population, or for being an ecological comparison study lacking individual-level data. A further 5 were dismissed as having “very serious methodological limitations”.
In their mechanistic assessment, the IOM reviewed 6 studies, but dismissed them all for not providing evidence beyond temporality, concluding that the mechanistic evidence is “lacking” when it comes to assessing a causal association between MMR and autism.
This left just 5 epidemiological studies that the IOM considered good enough to be used to conclude the lack of a causal association between MMR and autism. These were the studies by Taylor 1999, Farrington 2001, Madsen 2002, Smeeth 2004, and Mrozek-Budzyn 2010. The Mrozek-Budzyn study was acknowledged by the IOM as having “serious limitations”, and the Farrington study is based on the same data as the Taylor study.
I will review each of these MMR-autism studies in a future post.
Antigens-Autism Study
The CDC writes that:
A 2013 CDC study added to the research showing that vaccines do not cause ASD. The study looked at the number of antigens (substances in vaccines that cause the body’s immune system to produce disease-fighting antibodies) from vaccines during the first two years of life. The results showed that the total amount of antigen from vaccines received was the same between children with ASD and those that did not have ASD.
The De Stefano study is a helpful addition to the research, in that it looks at the cumulative effects of multiple vaccines, rather than at vaccines in isolation as in the IOM report.
However, the study is deeply flawed, because no one who claims that vaccines cause autism says that it should be related to the number of antigens received. It is the other ingredients of vaccines that are of greater concern, especially the aluminum salts used as adjuvants. Nevertheless, grouping by number of antigens has the potential to act as a proxy for distinguishing fully vaccinated, partially vaccinated, and unvaccinated, so it may not be an entirely worthless measurement.
Unfortunately, the results in the study are skewed by the presence of three vaccines with 3000 antigens (DTP, DTP-Hib, and Typhoid), and then a large drop down to vaccines with 69 antigens (Varicella), 24 antigens (MMR), and all other vaccines having less than 15 antigens. Total number of antigens is therefore merely a proxy for number of doses of high-antigenic vaccines. From the chart below it can be seen that most subjects had either zero, three, or four doses of these high-antigenic vaccines, and this alone determines the groups used in the analysis.
The chart also shows that there were no unvaccinated subjects in the study. Nobody received less than 50 antigens. The group that received zero high-antigenic vaccines received many other vaccines, because most of them had between 151 and 311 antigens. During the study period, the high-antigenic DTP vaccines were replaced by low-antigentic DTaP vaccines, so most of those in the “low antigens” group were fully vaccinated, just like most of the subjects in all the other groups.
At best, this study can be used to support the claim that high-antigenic vaccines do not cause autism any more than low-antigenic vaccines do. Since there are no high-antigenic vaccines used anymore, this is a moot conclusion. This study certainly cannot be used to support the claim that vaccines do not cause autism, because there were no unvaccinated subjects in the study.
Thimerosal-Autism Studies
The CDC then has a heading of “Vaccine ingredients do not cause autism” and writes that:
One vaccine ingredient that has been studied specifically is thimerosal, a mercury-based preservative used to prevent contamination of multidose vials of vaccines. Research shows that thimerosal does not cause ASD. In fact, a 2004 scientific review by the IOM concluded that “the evidence favors rejection of a causal relationship between thimerosal–containing vaccines and autism.” Since 2003, there have been nine CDC-funded or conducted studies that have found no link between thimerosal-containing vaccines and ASD, as well as no link between the measles, mumps, and rubella (MMR) vaccine and ASD in children.
That Institute of Medicine (IOM) report was called “Immunization Safety Review: Vaccines and Autism” (2004) and is a systematic review of all the epidemiology studies looking at associations between vaccines and autism. The report only examines studies of thimerosal-containing vaccines (TCVs) and the MMR vaccine (superceded by their 2012 review).
The IOM reviewed 12 studies looking for an association between TCVs and autism. 6 of them were dismissed for being based on data from a passive surveillance system lacking an unvaccinated comparison population, or for being an ecological comparison study lacking individual-level data. One study based on Vaccine Safety Datalink (VSD) data was dismissed as “uninterpretable”.
This left 5 studies on which the IOM relied for their conclusion that TCVs do not cause autism: Hviid 2003, Miller 2004, Verstraeten 2003, Madsen 2003, Stehr-Green 2003.
The CDC cites a two-page PDF that lists and briefly summarises eight further studies to support their claim TCVs do not cause autism: Barile 2011, Price 2010, Tozzi 2009, DeStefano 2009, McMahon 2008, Thompson 2007, Verstraeten 2003, Stehr-Green 2003 (included twice).
I will review each of these TCV-autism studies in a future post.
Thimerosal Removed From Vaccines
The CDC writes that:
Between 1999 and 2001, thimerosal was removed or reduced to trace amounts in all childhood vaccines except for some flu vaccines. This was done as part of a broader national effort to reduce all types of mercury exposure in children before studies were conducted that determined that thimerosal was not harmful. It was done as a precaution. Currently, the only childhood vaccines that contain thimerosal are flu vaccines packaged in multidose vials. Thimerosal-free alternatives are also available for flu vaccine.
Thus, the question of whether TCVs cause autism is now only of historical interest within the wider context of the question of whether vaccines cause autism. The studies cited to support that the claim that TCVs do not cause autism have significant weaknesses, and there is considerable evidence suggesting that TCVs do cause autism.
Since they are now rarely used, TCVs are clearly not an ingredient of concern to those who claim that vaccines cause autism today. Therefore, whether TCVs do cause autism is a moot point in respect of this present-tense claim.
“Other Ingredients”
Besides thimerosal, no other vaccine ingredients are named. All the ingredients in vaccines today are addressed by the CDC with a single sentence:
Besides thimerosal, some people have had concerns about other vaccine ingredients in relation to ASD as well. However, no links have been found between any vaccine ingredients and ASD.
No studies at all are cited to support this claim. The link goes to a page merely listing types of vaccine ingredients and their purpose:
Aluminum salts are the vaccine ingredient of biggest concern when it comes to autism, because aluminum is a neurotoxin that has been observed to induce subtle neurological effects and autism-like behaviour in animals exposed to it. The toxic nature of aluminum is why aluminum salt works as a vaccine adjuvant, ensuring that the activation of the immune system is strong enough to result in immunological memory.
There have also been health concerns raised about formaldehyde, glutamate, polysorbate-80, antibiotics, animal cells and fetal cells.
No studies are cited on this page to support the claim that vaccine ingredients do not cause autism.
“More Information”
The CDC provides a list of five links:
Facts About Autism Spectrum Disorders
Fact Sheet: Understanding Thimerosal, Mercury, and Vaccine Safety
IOM Report: Adverse Effects of Vaccines: Evidence and Causality, 2011
The first link has information about autism but not about vaccines. The second, fourth and fifth links are about TCVs. The third link is to the IOM 2011 Report cited above.
“Related Scientific Articles”
The CDC provides a list of seven links:
Taylor LE, Swerdfeger AL, Eslick GD. Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studiesexternal iconexternal icon. Vaccine. 2014 June;32(29):3623–3629.
Schechter R, Grether JK. Continuing increases in autism reported to California’s developmental services system: Mercury in retrogradeexternal icon. Arch Gen Psychiatry. 2008;65:19-24.
Institute of Medicine. Immunization Safety Review. Vaccines and Autismexternal icon Board of Health Promotion and Disease Prevention, Institute of Medicine (National Academy Press, Washington, DC, 2004).
Hviid A, Stellfeld M, Wohlfahrt J, Melbye M. Association between thimerosal-containing vaccine and autism pdf icon[PDF – 5 pages]external icon. JAMA. 2003;290:1763–6.
Madsen KM, Hviid A, Vestergaard M, Schendel D, Wohlfahrt J, et al. A population-based study of measles, mumps, and rubella vaccination and autismexternal icon. N Engl J Med. 2002;347 (19):1477–1482.
Ball L, Ball R, Pratt RD.An assessment of thimerosal in childhood vaccinesexternal icon. Pediatrics. 2001;107:1147–1154.
Joint statement of the American Academy of Pediatrics (AAP) and the United States Public Health Service (USPHS)external icon. Pediatrics. 1999;104:568–9.
The first link is to a meta-analysis that combined the results of five MMR-autism studies, and five TCV-autism studies, all of which individually found no associations. Most of the studies in this Taylor 2014 meta-analysis are the same papers reviewed by the IOM, cited above (including some they rejected for having serious methodological limitations); there is one new TCV study (Andrews 2004) and one new MMR study (Uno 2012).
The second link is to an ecological study, Schechter 2008, showing the removal of TCVs did not coincide with any reduction of cases of autism in California. The third link is to the IOM 2004 Report cited above. The fourth link is to the Hviid 2003 study of TCVs-autism. The fifth link is to the Madsen 2002 study of MMR-autism, both in the IOM Reports cited above. The sixth link is to an outdated review of TCVs that does not reference autism. The seventh link is to a statement by the AAP regarding removing thimerosal from vaccines.
Conclusion
There is no evidence cited on the CDC’s “Autism and Vaccines” page to support their claim that vaccines do not cause autism. The only evidence cited relates either to one single vaccine: the MMR, or to one single vaccine ingredient: thimerosal. Even if this evidence is accepted, it does not follow that vaccines do not cause autism.
More studies are needed in order to determine whether vaccines cause autism, starting with the most basic kind: epidemiological studies that compare health outcomes in vaccinated and unvaccinated children.
Interestingly, this was pointed out by the IOM itself in their 2013 report “The Childhood Immunization Schedule and Safety”:
Without any studies looking at autism as a health outcome and comparing vaccinated and unvaccinated groups, there is no support for the CDC’s claim that vaccines do not cause autism. They were right to change the title of their page. They now need to correct the rest of it.