The Illusory Link Between Vaccinations and Autism

This month my second son celebrated his very first birthday. For many families, a child’s first birthday is celebrated with cake, balloons, and presents. My son’s was too, but for me, the birthday present I was most excited to give him was not at his party, but at his 1-year well-visit to the pediatrician. Usually these visits are mostly an annoyance and something I put off scheduling, but this particular visit couldn’t come fast enough. This time, he’d get his MMR vaccine for measles, mumps, and rubella. Not exactly the gift he was most excited about receiving, but it was definitely the one I was happiest to give him. Current measles outbreaks in Washington State and New York , where we live, have caused a lot of anxiety for parents. In recent years, a large increase in the number of parents who are refusing to vaccinate their children has resulted in less protection against diseases like the measles not only for the unvaccinated children, but also for infants like mine who are still too young to receive vaccinations like the MMR.

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Questions about the safety of vaccinations started about a decade ago after medical researcher Andrew Wakefield and his colleagues published a paper reporting that vaccinations—and specifically the MMR vaccine—were linked to autism (Wakefield et al., 1998). The paper startled a lot of people in the scientific community and as you can imagine, terrified many parents. Luckily the scare was all for naught; it turned out that Wakefield made up his data, and the paper was later retracted. In fact, he ended up losing his job and medical license because of it. Unfortunately, the news of his results, although fake, already spread to parents around the world; vaccination rates began to drop, and the incidence of illnesses that were nearly obsolete like measles and whooping cough started to soar as more and more parents chose not to vaccinate their children. As a result, here we are, with measles outbreaks in the United States and in other countries, most recently the Philippines . In fact, the number of measles cases has gotten so large in Washington that the governor declared a state of emergency .

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Following Wakefield’s study, other researchers tried to find a link between vaccinations and autism and every one of them has failed (e.g., Maglione et al., 2014; Taylor, Swerdfeger, & Eslick, 2014). In fact, there is absolutely no scientific evidence that vaccinations cause autism . None. So why are so many people still choosing not to vaccinate? First, there is the unfortunate coincidence that warning signs of autism—not responding to their name, not babbling, little eye contact—often become obvious around the same time that infants get a hefty round of vaccinations, especially around their first birthday. The timing makes the link (although illusory) seem very real. Fear is also a powerful motivator. Parents want to do the best they can to protect their kids from getting hurt or sick, and hearing anyone talk about a link between vaccinations and autism or any other side effect can be quite rattling, especially when it comes from celebrities that have a very public platform to voice their concerns.

Further, concern about autism is not the only reason parents are choosing not to vaccinate. Many forego vaccinations because of their religious beliefs. Others—possibly still as the result of Wakefield’s study—are wary of putting certain chemicals into their children’s bodies; they think that the risk for contracting diseases like the measles are so minimal that they don’t need to vaccinate, or they think the risks of vaccinating outweigh the benefits. On top of that, there are other parents who aren’t necessarily anti-vax, but don’t have enough information about vaccinations to make a comfortable decision either way (McKee & Bohannon, 2016).

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What actually causes autism? Scientists don’t yet know for sure, but it is likely an interaction between a strong genetic predisposition and some environmental circumstances. Researchers often investigate the role of genetics in causing an illness by studying groups of identical and fraternal twins. Identical twins have the same genes, and grow up in a similar environment. Fraternal twins are like siblings—they only share some of the same genes, and also grow up in a similar environment. If genes play a role in producing an illness or developmental disability, you would expect the concordance rate—or the likelihood that both twins have the same illness—to be higher in identical versus fraternal twins. If illnesses are purely caused by something in the environment, like a vaccine, you’d expect the concordance rate for an illness to be the same for identical versus fraternal twins.

Researchers from Great Britain recently applied this logic to studying the incidence of autism, or Autism Spectrum Disorder (ASD) diagnoses in various groups of twins. They found that genetic factors accounted for up to 95% of the incidence of autism in their subjects (Colvert et al., 2015). This suggests that genetics plays a pretty big role in determining whether someone ends up developing ASD. But genes didn’t account for 100% of the incidence of autism, so there is some room for environmental risk as well. Research has pointed to several risk factors that are associated with the incidence autism, including advanced parental age (Durkin et al., 2008), premature birth (Leavey, Zwaigenbaum, Heavner, & Burstyn, 2013), closely spaced pregnancies (Cheslack-Postava & Liu, 2011), the presence of some viral infections in mothers during pregnancy (Atladóttir et al., 2010; Zerbo et al., 2013), and gestational diabetes (Xiang et al., 2015). In contrast, taking prenatal vitamins while pregnant is associated with decreased risk for autism in a child (Schmidt et al., 2011). None of these things directly cause autism (or prevent it), but they are all associated with different levels of risk, and it’s likely that some combination of genetic and environmental risk factors all put together in the same person is what ultimately causes symptoms of autism to emerge. Importantly, those combinations of factors might differ between individuals, and in fact, the behaviors associated with ASD can vary immensely from one person to another, so it’s difficult for researchers to pinpoint a combination of factors that best predict the emergence of ASD in most affected children.

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The take home message here is that there is no evidence that vaccinations cause autism, or brain damage, or any other dangerous illness. Vaccinations aren’t even associated with increased risk of autism, like some of the other factors listed above. Instead, ASD is likely the result of a complicated interaction of both genetic and environmental factors that are often out of our control. Vaccinations do have some potential side effects, but those side effects are all relatively rare, and generally quite mild (e.g., fever, headache, joint pain). And perhaps most importantly, while there’s no evidence that vaccinations increase the risk of autism, there’s a great deal of evidence that vaccinations are highly effective at preventing disease (up to 95%). Not getting vaccinated is incredibly risky if your child is exposed to a serious and preventable illness, which is becoming more and more likely with recent outbreaks. So, it is the consensus among the vast majority of doctors and scientists that the risks of vaccinating (which again are rare and generally mild) do not outweigh its immense benefits, which include protecting your child from illnesses like chicken pox, whooping cough, a measles outbreak, and even more potentially dangerous illnesses like tuberculosis, meningitis, and polio (Gust et al., 2008). It’s also important to remember that vaccinations are most effective when we all do it, and choosing not to vaccinate your children not only puts them but also many others—including infants who are not yet old enough for certain vaccines—at serious risk.