As Supreme Court Eyes Vaccines/Autism Debate, the Science Points Only One Way

While the Supreme Court ponders the issue of whether vaccines cause autism -- and therefore whether drug companies should be held liable in federal courts if that were so -- it's worth looking at the evidence on both sides for the notion that vaccines, or the thimerosal preservative that is no longer used in them, causes autism. That evidence is disputed by groups like SafeMinds and Age of Autism, which are currently trying to persuade movie theater owners to run an ad urging parents not to get their children vaccinated against the flu. The ad sounds reasonable enough -- until you spend some time picking through the research.

One of the mysteries about this debate is why so many Americans continue to believe that vaccines cause neurological damage to babies even when they are presented with evidence that the opposite is true. A good example of this stubbornness can be seen in an old Pharmalot item from 2007. It's a report on a New England Journal of Medicine study that showed there was no link between thimerosal and autism* neuropsychological damage. Underneath the item, Pharmalot's Ed Silverman ran a poll in which readers were asked, "Do you feel reassured by the study?" At the time of writing, 90 percent of respondents answered "no."

Part of the reason this illogical phenomenon exists is, arguably, a lack of scientific literacy in America. Science isn't well taught here, and we're not good at learning it either. Children in Hungary, the Czech Republic and Slovenia all understand science and math better than our students. The U.S. isn't even in the top 10 nations for eighth-grade science and math knowledge. (We're eighth -- behind Latvia! -- at the fourth-grade level.)

In the vaccine-autism debate specifically, the crucial difference between the two sides is how you understand the science and the math being presented. The anti-vaccine crowd often relies on small, anecdotal studies with few subjects. Many of these studies are of animals or cell cultures rather than actual humans. The pro-vaccine crowd, by contrast, relies on very large studies, some with millions of children.

This difference is important because of the level of statistical significance afforded to them. Put simply, the more subjects in a study, the more likely it is to be right. The fewer subjects, the more likely it is to be wrong. If you do a clinical trial with 200 patients, you only need to show accidental bias or make some data-entry mistakes on a handful of those subjects in order to skew the data in a way that appears to be statistically significant. But when you've got 1,000 people or more in your trial only genuine trends -- or baseline errors or fraud -- will skew the results. (In fact, research fraud has cropped up in two of the studies that anti-vaccine activists have frequently cited to make their case: The Wakefield-Lancet study of 1998 and the O'Leary case in Ireland.)

What follows is a selection of studies from both sides. It's not possible to reproduce all the studies in this field -- there are thousands of them -- but the ones listed here are typical. You'll see that the anti-vaccine research is generally small scale, whereas the pro-vaccine research has been done on a massive scale. If you want to base your opinions on the best evidence available, then the best evidence favors the fact that vaccines don't cause autism. As the CDC puts it:

Research does not show any link between thimerosal in vaccines and autism, a neurodevelopmental disorder. Although thimerosal was taken out of childhood vaccines in 2001, autism rates have gone up, which is the opposite of what would be expected if thimerosal caused autism.

• A study of 41 monkeys exposed to vaccines containing thimerosal.
• A cell culture study of thimerosal as a neurotoxin.
• A study of cell development and thimerosal as a neurotoxin.
• A study of 284 children with autism spectrum disorder and 657 control children
• You can read many more of these studies here and here and here (under the tab marked "Autism Conditions & Related Medical Conditions").

• Study showing that children who get vaccines on time in the first year of life do better than those who don't.
• A study of 124,170 infants who were born during 1992 to 1999.
• A study of all children born in Denmark from January 1, 1990, until December 31, 1996 -- 467,450 kids.
• A study of all children between 2 and 10 years old who were diagnosed with autism during the period from 1971-2000 in Denmark.
• A study of the national childhood vaccination records for the entire populations of the U.S., Sweden, and Denmark from the mid 1980s to the late 1990s.
• The eighth Institutes of Medicine study on this issue provides a great literature review of both sides of this debate, and concludes there is no link.
• You can see more of this type of study here and here and here.

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