One of the most popular claims in the anti-vaccination literature is that vaccines (often the MMR vaccine) are linked to autism1. This claim has gotten even more popular since Dan Burton’s Congressional committee has held hearings on this subject. However, Congressional hearings are hardly scientific forums, given the fact that such environmental experts as Meryl Streep testify before Congress on the effects of pesticides2, and biochemistry luminaries like Ben Affleck3 testify before Congress on current advances in genetics. Congressional hearings are forums for disgruntled citizens to make impassioned pleas and for craven politicians to “perform” for their constituents. If you want to know the truth about medicine, you must look at the medical literature, and the medical literature is quite clear – there is no link between vaccines and autism.
Let’s start with the idea that the MMR is somehow linked to autism. Taylor and others4 looked at autism cases in the United Kingdom from 1979 to 1999. Since the MMR vaccine was introduced in the UK in 1988, this study encompassed 9 years prior to use of the MMR and 11 years after its use began. They found that the autism rates increased steadily from 1979 to 1999, with no increase in the rate after the MMR was introduced. If the MMR were linked to autism, you would expect a “bump” in the autism rate shortly after the MMR became widely-used. No such “bump” occurred. Also, comparing vaccinated children to unvaccinated children, there was no difference in the average age at which diagnosis occurred. If the MMR were linked to vaccination, you would expect that the vaccinated children’s autism would occur nearer to the vaccination as compared to unvaccinated children. This was not the case.
In a similar study, Dales and others5 looked at the number of autism cases in California from 1980 to 1994. They also looked at the rate of MMR vaccination over the same time period. Here is what they found:
Notice that there is no correlation between the number of autism cases and the vaccination rate. The vaccination rate of those at or under the age of 17 months increased by roughly 50% over the period, while the number of autism cases increased by 600%. Also, if you look at the date range of 1988 to 1994, you will see that the vaccination rate of those at or under the age of 17 months barely changed at all, while the number of autism cases increased by 300%. The data are even more striking for the vaccination rate of those at or under the age of 24 months. That vaccination rate barely changed over the entire time period, but the number of autism cases increased by 600%.
These data are fairly straightforward. There seems to be no association between the MMR and autism. It also illustrates another lie told by many anti-vaccination advocates. They often claim that the number of autism cases have increased as the vaccination rates have increased. These data show that such a claim is simply wrong. Autism rates have skyrocketed as vaccination rates have barely changed.
In a more direct study, Madsen and others6 examined all children (more than half a million) born in Denmark from 1991 through 1998. Of those children, 82 percent had received the MMR vaccine. The other 18% had not. The researchers found that there was no difference between the autism rate of vaccinated children as compared to unvaccinated children. In such a large study, even a slight increase in the risk of autism due to the MMR vaccine would show up. However, no such increase was seen. This is strong evidence that the MMR vaccine is not linked to autism.
The thought that vaccines are somehow linked to autism has also come about due to the fact that a mercury-containing compound (thimerosal), is sometimes used as a vaccine preservative. As a result, when a person gets certain vaccines, he also gets a small dose of mercury. Since high doses of mercury have been linked to neurological problems, there are those who think that the small amount of mercury in some vaccines can cause neurological problems such as autism. However, several studies have been done specifically looking for a link between the thimerosal in vaccines and autism, and none can be found.
For example, Heron and others7 studied almost 13,000 children in the United Kingdom. They tracked the amount of mercury the children were exposed to through vaccination as well as other sources (such as the consumption of fish). They also examined many other factors that lead to developmental disorders. When they adjusted for all of those factors, they found no link between thimerosal exposure and developmental disorders, including autism.
Probably the most convincing study showing that thimerosal is not linked with vaccination comes from Denmark8 , where all thimerosal-containing vaccines were discontinued in 1992. The study looked at all autism cases diagnosed from 1971 to the year 2000. The results indicate that the number of autism cases was fairly steady until 1990, and after that, it rose steadily throughout the study period. If thimerosal were to blame for autism, you would expect the number of autism cases to drop, remain steady, or at least not increase as dramatically after 1992, when the use of thimerosal-containing vaccines was discontinued. That did not happen. Thus, autism is simply not related to thimerosal exposure through vaccination.
Many studies using many methodologies have been done trying to link vaccines or the thimerosal contained in some of them to autism, and the link is simply not supported by the data. Just recently, the Institute of Medicine examined all available studies on autism and vaccination. Five large studies conducted in the U.S., Denmark, the U.K., and Sweden since 2001 showed no link between thimerosal-containing vaccines and autism. In addition, 14 large epidemiological studies showed no link between the MMR and autism. A few studies showed a tenuous link between vaccines and autism, but each study had flaws, and none of them were nearly as large or far-ranging as the studies that showed no link. Thus, the vast majority of the data show that there is simply no link between vaccines and autism. This is why the Institute of Medicine clearly states, “The committee concludes that the body of epidemiological evidence favors rejection of a causal relationship between the MMR vaccine and autism. The committee also concludes that the body of epidemiological evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism.”9 In other words, the data clearly say that vaccines are not related to autism.
In fact, the latest research indicates that autism is a genetic disorder. A French team of scientists10 has identified two mutated genes that appear to cause autism. Both genes are located on the X-chromosome, which makes sense, since autism is four times more prevalent in men than women. Since women have two X-chromosomes, they are less likely to be affected by a mutated gene on that chromosome. After all, a woman would have to acquire one mutated gene from her mother and another mutated gene from her father to be affected. This is rather unlikely. On the other hand, a man needs only inherit one mutated gene on the X-chromosome, and he will be affected by the gene.
What do these genes do? They tell the cell to produce proteins called “neuroligins,” which appear on the junctions between nerve cells. These junctions are called “synapses,” and they allow nerve cells to communicate with one another. Neuroligins are crucial for the proper function of a synapse. Thus, if a neuroligin is not made properly because the gene that codes for its production is mutated, it makes sense that the person affected by such a gene would have a neurological disorder.
The sad thing about the anti-vaccination advocates’ lies regarding vaccines and autism is that they have distracted medical researchers from finding the real cause of autism. Let’s hope that no more distractions occur and that medical researchers can do what they should have been doing all along. That’s the hope of Dr. Peter J. Hotez, whose son has autism. He not only knows the challenges of having a child with autism, he also knows the medical research behind the condition. You can read his rebuke of the anti-vaccination movement here.
1. See, for example, (Think Twice) Return to Text
2. Health Effects of Pesticide Use On Children: Hearing Before the Subcomm. on Children, Family, Drugs and Alcoholism of the Senate Comm. on Labor & Human Resources, 101st Cong., 1st Sess. 32 (1989)28 Return to Text
3. Promise of the genomic revolution : hearing before a subcommittee of the Committee on Appropriations, United States Senate, One Hundred Seventh Congress, first session, special hearing, July 11, 2001, Washington, DC. Return to Text
4. Taylor B, et al. “Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association” Lancet 1999;353:2026-9 Return to Text
5. Dales, L, et al., “Time Trends in Autism and in MMR Immunization Coverage in California” JAMA 2001;285:1183-5 Return to Text
6. Kreesten Meldgaard Madsen, et al. “A Population-Based Study of Measles, Mumps, and Rubella Vaccination and Autism” NEJM 2002;347:1477-1482 Return to Text
7. Heron J, et al. “Thimerosal Exposure in Infants and Developmental Disorders: A Prospective Cohort Study in the United Kingdom Does Not Support a Causal Association. ” Pediatrics 2004;114: 577-583 Return to Text
8. Kreesten Meldgaard Madsen, et al. “Thimerosal and the Occurrence of Autism: Negative Ecological Evidence from Danish Population-Based Data. ” Pediatrics 2003;112: 604-6 Return to Text
9. Institute of Medicine Immunization Safety Review: Vaccines and Autism 2004, p. 1 (Available online) Return to Text
10. Jamain S, et al., “Mutations of the X-linked genes encoding neuroligins NLGN3 and NLGN4 are associated with autism” Nat Genet. 2003;34(1):27-9 Return to Text
Dr. Wile is not a medical doctor. He is a nuclear chemist. As a result, he does not dispense medical advice. He simply educates the public about scientific issues. Please consult a board-certified medical doctor before making any medical decisions for yourself or your family.