We Already Have Evidence That the MMR Vaccine Does Not Cause Autism

Peer-reviewed research reports almost always end with some version of the same statement: “More research is needed to confirm the findings presented by this study.” No matter how impressive a finding may be, scientists almost always caution that there are still unanswered questions and the need to replicate what has been found.

Yet, in some cases, it is time to stop research. The alleged relationship between autism spectrum disorder (a.k.a. autism or ASD) and the vaccine against measles, mumps, and rubella (MMR) is one of them. Unfortunately, the US Centers for Disease Control and Prevention (CDC) has announced it will fund a new study to examine whether there is such a connection, pointing to the clear rise in cases of ASD diagnosed among U.S. children and promising answers by this fall. Media reports about this announcement noted that the idea of such an association has been disproven, but it may surprise some to know just how thoroughly disproven it really is.

The Evidence Is Overwhelming

Jessica Steier and her colleagues at Unbiased Science reviewed the literature on the claimed connection between the MMR vaccine and autism and concluded that “More than 20 major studies involving over 10 million children across multiple countries, populations, and decades have found that there is no link between vaccines and autism.” They also noted that these studies used a variety of research methods.

This is a staggering amount of evidence against any connection between the MMR vaccine and ASD, and there is no reason to gather more data. To do so will only further undermine the public’s confidence in vaccines and waste precious taxpayer dollars.

More Research in the Right Areas

Source: CDC / Unsplash

So what kind of research should we be doing to better understand autism? First, we need to dispel the myth that the rise in autism rates has anything to do with an environmental toxin that the planned new research project will uncover, as has been suggested by current government officials. While it is true that ASD rates are rising—to about 1 in 31 children according to CDC data released earlier this year—all experts agree that this does not represent a new “epidemic.” Rather, as the American Psychological Association put it, “the increasing diagnosis of autism can be explained by the adoption of better diagnostic tools, changes in definitions, changes in screening practices, new policies, and improved advocacy and education.” In fact, current diagnostic methods may be underestimating the number of girls who would qualify for a diagnosis of ASD. Given the rapid changes in diagnostic criteria and methods for autism, there is still more work to be done to determine how best to evaluate children for an ASD diagnosis.

Even more pressing is the critical need to push forward on high-quality research into the causes of autism. It now appears that the major influence over whether a child will be diagnosed with ASD is genetic. When a mutation in a single gene is not the likely cause, scientists must use complicated methods to determine how much of any human feature is related to inheritance. One way to do this is to look at something called concordance between identical and fraternal twins.

Because identical (or monozygotic) twins share all the same DNA and therefore have identical genes, if something is purely genetic, then if one twin has it, the other must almost always have it as well. This is true for traits like eye color and blood type and illnesses caused by genetic mutations like Huntington’s disease and sickle cell anemia. This is called 100 percent concordance. On the other hand, because fraternal (or dizygotic) twins share only 50 percent of the same DNA (like regular siblings), we expect that if one twin has a trait, the other will also have it about half the time. In both cases, it does not matter whether the twins are raised together or apart; concordance rates should be about 100 percent for identical twins and 50 percent for fraternal twins.

But if a trait or illness is caused entirely by an environmental event, like an infection or accidental injury, then it makes a big difference if twins are raised together or apart. Twins raised together will tend to be exposed to the same environmental influences, whereas when raised apart, those influences will be different. Take getting the flu, for example. Twins raised together will tend to both be exposed to the influenza virus at about the same rate, so the concordance rate between identical and fraternal twins will be nearly equivalent and approach 100 percent for both. If the twins are raised apart, however, the concordance rates will be much lower than 100 percent for both types because, in this case, only one twin in the pair will be exposed to the environmental influence.

By comparing concordance rates among identical and fraternal twins raised apart and together, scientists can estimate the percentage of influence that genes and the environment have over any trait or condition. F. Perry Wilson, a professor of medicine and public health at Yale, looked at twin studies for autism, and what he found is striking. “Concordance rates among identical twins range from 60%-90% and, for fraternal twins, from about 3% to 30%,” he concluded. “That’s a strong genetic signal.” Overall, experts agree that autism is 60 to 90 percent a heritable condition. That means that one clear avenue for research is to try to find exactly what genes are involved. This won’t be easy because, as is the case for most things involving the brain, it is highly unlikely that a single gene is involved. Rather, multiple genes, each having a small effect, are probably behind who inherits a diagnosis of ASD. Fortunately, modern geneticists have sophisticated epidemiological and biological techniques available to try to unravel the genetic side of autism, and this is clearly an area where federal research dollars should be applied.

Still Room for the Environment

That also leaves plenty of room for environmental influences for autism, and many have been suggested but not proven yet. Among the candidates so far are prenatal factors, including the health of the pregnant person, advanced parental age, air pollution, and exposure to pesticides. And this is only a partial list of the many things that association studies have linked to autism. Once again, it is important to stress that vaccines are not among them. Sorting through these factors and figuring out how much of a contribution each makes to autism deserves research attention and funding.

Autism Essential Reads

Meeting People as Individuals, Not Assumptions

Autism Barbie? I’m Not a Fan

Ironically, although Secretary of Health and Human Services Robert F. Kennedy Jr. pledged $50 million to find the “environmental toxin” he believes is behind autism, one analysis suggests that federal funding for autism research has actually been cut by $31 million by the present administration, and more cuts may be in store.

Of course, the recently proposed autism research won’t really yield much legitimate new information by this fall. Scientists have been laboring for decades to unravel the complexities of ASD. They know that it is indeed a spectrum—a condition that varies enormously in its characteristics from individual to individual. They also know it is largely an inherited condition, but that environmental factors also play an important role. They have worked to understand stigma regarding autism and to develop evidence-based approaches to eliminating biases. Science has also advanced the ways that we categorize, evaluate, and diagnose ASD and developed evidence-based approaches for interventions when those are deemed necessary. Clearly, we do not want to stifle further progress by the distraction of pursuing an avenue that is an obvious dead end. Vaccines have nothing to do with autism. It is time to lay that idea to rest and prevent the further waste of scientific time and money.