Pictured: not a risk of autism

Pictured: not a risk of autism

A new study published this week in JAMA, “Autism Occurrence by MMR Vaccine Status Among US Children With Older Siblings With and Without Autism”, puts one more nail in the claim that the MMR is associated with autism.

You may wonder why, after years and multiple studies showing no association between the measles-mumps-rubella vaccine (MMR) and autism spectrum disorder (ASD) there would even be a need for such a study. The authors explain:

Despite research showing no link between the measles-mumps-rubella (MMR) vaccine and autism spectrum disorders (ASD), beliefs that the vaccine causes autism persist, leading to lower vaccination levels. Parents who already have a child with ASD may be especially wary of vaccinations.

The study is a retrospective cohort study involving 95,727 children with older siblings. They looked at whether or not the older sibling had a diagnosis of ASD, whether or not they were vaccinated with MMR, and whether or not they themselves developed ASD. They found:

MMR vaccination rates (≥1 dose) were 84% (n = 78 564) at age 2 years and 92% (n = 86 063) at age 5 years for children with unaffected older siblings, vs 73% (n = 1409) at age 2 years and 86% (n = 1660) at age 5 years for children with affected siblings. MMR vaccine receipt was not associated with an increased risk of ASD at any age. For children with older siblings with ASD, at age 2, the adjusted relative risk (RR) of ASD for 1 dose of MMR vaccine vs no vaccine was 0.76 (95% CI, 0.49-1.18;P = .22), and at age 5, the RR of ASD for 2 doses compared with no vaccine was 0.56 (95% CI, 0.31-1.01; P = .052). For children whose older siblings did not have ASD, at age 2, the adjusted RR of ASD for 1 dose was 0.91 (95% CI, 0.67-1.20; P = .50) and at age 5, the RR of ASD for 2 doses was 1.12 (95% CI, 0.78-1.59; P = .55).

Children with older siblings with ASD were less likely to be vaccinated, presumably because of parental fear of an association. The results clearly show, however, no association between the MMR vaccine and the risk of developing ASD, for children with or without an older sibling with ASD.

This study directly addresses the claim by some in the anti-vaccine movement that vaccines may trigger autism in susceptible individuals. This was little more than special pleading, however, after evidence showed no overall link between MMR and ASD.

In January 2015 a smaller case-control study looked at early MMR and thimerosal exposure among children with ASD and without and found no difference. (A cohort study, like the one above, looks at different groups and then assesses whether or not they develop a disease. A case-control study compares those with the disease to those without for some possible risk factor.)

A 2014 systematic review found:

There is strong evidence that MMR vaccine [sic] is not associated with autism.

Overall they found that serious side effects from the vaccine were extremely rare.

A separate 2014 systematic review and meta-analysis concluded:

Findings of this meta-analysis suggest that vaccinations are not associated with the development of autism or autism spectrum disorder. Furthermore, the components of the vaccines (thimerosal or mercury) or multiple vaccines (MMR) are not associated with the development of autism or autism spectrum disorder.

The evidence at this point is overwhelming – every way this data has been crunched the same answer emerges, there is no link between vaccines in general, thimerosal, or the MMR specifically, with autism or ASD.

While further study is not necessary, every study does increase our confidence significantly. However, we are beyond the point where, from a scientific point of view, spending further resources to ask and answer the same question is dubious at best. In fact, it can be considered a waste of limited research resources. This is not a small thing, as any researcher desperate for funding can tell you.

This is part of the damage of the anti-vaccine movement, and proponents of pseudoscience in general. Society is best served if our limited research resources are spent to maximal effect, improving the science and practice of medicine, and our understanding of science in general.

I think it can be reasonably argued that all research resources spent on “alternative” medicine, or chasing wild conspiracy theories or crank ideas, represent a massive inefficiency, slowing the rate of scientific progress. Such research is justified, as is the current study, by addressing popular opinion, rather than scientific plausibility or prior probability. “Popular” opinion often means a vocal minority.

I am not saying we should never do such research. Medicine is an applied science, and sometimes we need to provide research to address a public, rather than a scientific, concern. But it should be recognized that research is probably a fairly ineffective means of addressing such concerns. Anti-vaxxers are unlikely to be swayed by new evidence, just as conspiracy theorists are immune to evidence. Likewise, CAM proponents never abandon treatments because research shows they are ineffective (I have yet to see a counter-example, and have an open challenge to anyone who can point to one).

It seems to me that if we are going to spend limited resources to study a question in order to reassure a public concern, then we should endeavor to ascertain whether or not the concern is eased by the research. History indicates that it largely isn’t. One possible solution to this dilemma is to tie such research funding to specific regulatory measures.

For example, the government could fund research into CAM treatments, but only if those treatments are properly regulated, so that the research results can be implemented rather than ignored. Research into vaccine safety (above and beyond what is scientifically necessary) can be tied to laws removing vaccine exemptions if those vaccines are found to be safe.

In addition to having a regulatory environment in which the results of this research will actually be used, we should not rely on research as the only means of addressing public non-scientific beliefs and concerns. Improved education and outreach is another approach, which means that scientists and academic institutions need to get more proactive in managing public scientific literacy and understanding of specific issues, like vaccine safety.

Without proper regulation and outreach, research dollars into answered questions or unlikely treatments are thrown down a black hole and utterly wasted. Add this to the list the next time someone asks, “what’s the harm?” with regard to pseudoscience.

 

 

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the president and co-founder of the New England Skeptical Society, the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also contributes every Sunday to The Rogues Gallery, the official blog of the SGU.