Despite my high tolerance for people with differing opinions, I tend to stay away from vaccination debates. It's one of the few topics that just makes my poor public health statistician brain go from calm to exploded in two seconds. Nevertheless, when Scott (over at Lawyers, Guns, and Money) posted this from Obama, "We've seen just a skyrocketing autism rate. Some people are suspicious that it's connected to the vaccines. This person included. The science right now is inconclusive, but we have to research it." (updated with the news that Clinton is skeptical of vaccines too) I just couldn't stop myself from diving in. First, let me say THE SCIENCE IS NOT INCONCLUSIVE!!!! But, as I commented over at LGM, I can see how this is one of those cases where the mainstream interpretation of specific scientific results is getting muddied. Scott was nice enough to pop my comment up to the main page, and I'm lazy, so I'll just copy it here:
In particular, no study can ever 'disprove' much of anything. All it can do (and many, many studies consistently have, in this case) is fail to find a link. In statistical terms we always call this 'failing to reject the null hypothesis of no relationship.' It's a weird double negative, but it's careful for a reason - we always set up our experiments assuming the thing we're trying to disprove is true. Our conclusion options are to reject the null (and conclude that a relationship exists) or fail to reject the null. We typically shy away from clearly stating that this means conclusively that no relationship exists, since as scientists we're always open to the possibility of being wrong - perhaps another study will come along with better/different methodology and contradict our findings, perhaps someone will have more money and more time and collect more data and contradict our findings, etc. However, all that hemming aside, just like a scientific theory is treated with more confidence than the layman interpretation of the word 'theory,' when numerous studies consistently fail to reject the null hypothesis, most reasonable scientists are comfortable assuming that this means that no relationship exists.
A little easy digging around via google and it becomes clear that there is a consensus among scientists:
- This page from the National Institute of Allergy and Infectious Diseases is a nice summary of current research regarding thimerosal, in particular how it is different from methyl mercury.
- This page from the CDC summarizes research into autism and vaccines being conducted by the CDC, the National Institutes of Health, the Institute of Medicine, the National Institute of Child Health and Human Development, the National Institute of Allergy and Infectious Diseases, and the Food and Drug Administration.
- This CDC page includes a FAQ about autism and vaccines, including these important statements:
To date, there is no conclusive evidence that any vaccine increases the risk of developing autism or any other behavior disorder.
Several epidemiological studies show no causal association between the measles/ mumps/ rubella (MMR) vaccine (or other measles-containing vaccines) and autism. In January 1990, the Institute of Medicine (IOM) concluded that there was no evidence to indicate a causal relationship between autism and the diphtheria/tetanus/pertussis (DTP) vaccine or the pertussis component of the DTP vaccine. In 2001, the IOM concluded that there is no causal relationship, at a population level, between the MMR vaccine and ASDs. (ASD = Autism Spectrum Disorder, which includes a range of developmental issues.)
- And lastly, this table from the CDC is a nice summary of all the research currently out there, including references to specific journal publications.
I can predict your next question - but what about Hannah Poling? (the young girl whose family was recently awarded a financial settlement from the federal government) Let me be very clear - Hannah Poling had a very specific, and extremely rare, underlying mitochondrial disease that may have been exacerbated by a fever resulting from her vaccinations. It is, of course, very sad whenever a child is sick, and I don't mean to downplay the tragedy of her case. But what do you suppose the odds are that she would have suffered a fever, from some cause, any cause, at some point in her life, that would have exacerbated her underlying condition? She had a genetic predisposition toward autism, and unfortunately her childhood vaccines provided the stress to her system that caused her disease to manifest. There are any number of other plausible stresses that could have come along in her life and resulted in the same thing. Her case does not mean that there is an inherent link between vaccines and autism, or that your child is at an elevated risk of negative side effects from vaccines.
And yes, there is a risk of side effects from vaccines. They do stress your system, many children do develop low-grade fevers and other minor symptoms. In the vast majority of otherwise healthy children, this is a trivial cost to pay compared to what happens to kids who catch measles or mumps or whooping cough. There are a number of perfectly valid, medical reasons why a small number of children should not be vaccinated. Of course, every responsible parent should discuss his or her child with his or her doctor to be as confident as possible that your child does not have a rare underlying condition that may put him or her at additional risk from the small amount of stress caused by vaccines. But in general vaccines prevent so much more harm than they cause. I know it's scary to talk about risk-benefits when it's your kid sitting on the table, but try to weigh the very real chance that your child will be exposed to a potentially life-threatening disease like measles or whooping cough (or will expose another person's child) against the very, very small chance that your child has some incredibly rare underlying disorder, which may be just as likely to manifest as the result of a normal childhood cold as it is the result of a vaccine.
And lastly, autism is, of course, a very real, and tragic problem. I don't want to downplay how difficult it must be to have a child with autism. But all the more reason to expend time and energy and money on identifying the real culprit - be it genetics or environmental exposures or some combination, and finding treatments that work and hopefully, one day, a cure. We've chased down this possibility, like good scientists we have found it not to be a plausible explanation of a real problem, so let's quit wasting money on it.