Tuesday, September 22, 2009

The Autism Vaccine Wars

For those of you who missed the opening battle in the autism vaccine wars and wanted a cliff notes version there is a recent paper in Neurotoxicity Research that gives a good summary. This paper is freely available, so I encourage everyone who is interested to read it for themselves.

Are Neuropathological Conditions Relevant to Ethylmercury Exposure?

As most of you know there are two forms of mercury at issue here. The first is called methylmercury and is the type that makes up the majority of our exposure to mercury. We are exposed to this type from the environment and the food that we eat. Science has a good idea of how the body responds to this form of mercury and what its affects are.

Then you have the second type of mercury, known as ethylmercury. Vaccines contained a substance called thimerosal that is metabolized by the body into ethylmercury. We do not know as much about how this form of mercury acts in the body and therein lies the problem.

Around 1999 someone in the US looked at the vaccine schedule, did some basic math, and came to the conclusion that children were receiving far more ethylmercury than was realized. Since there are no specific safety guidelines for ethylmercury, they used the next thing, the guidelines for methylmercury. And according to these guidelines, the combined does that children were receiving was well over the safety limit.

As would be expected, panic ensued. Two years later it was recommended that thimerosal be removed from vaccinations, and today most vaccines are thimerosal free.

This was the first major battle in the autism-vaccine wars which continue to this day. With that in mind, lets consider this paper.

The authors start out by giving a brief history of mercury and its use in vaccinations. If you don't know the history then it is worth reading this paper for that alone. Just keep in mind where the authors are coming from and that they are glossing over some inconvenient details.

The authors make the the point that the properties of ethylmercury were not understood in 2001 when the decision to remove it from vaccinations was made. It was assumed that this form of mercury acted the same way that methlymercury. However, subsequent research has shown that this assumption is not valid and that ethylmercury acts differently in the body than methylmercury. As a result, our initial concerns were most likely unfounded and thimerosal in vaccines does not cause developmental disorders.

The authors give three specific ways that ethylmercury differs from methlymercury :
  1. Ethylmercury clears from the body much faster than methylmercury.
  2. Ethylmercury does not deposit as much mercury in the brain as methylmercury.
  3. Ethylmercury decomposes much faster than methylmercury.
The authors go into great detail for each reason, citing multiple studies and building a careful, rational argument for each of their points. I am not going to talk about the underlying reasons as I think they are mostly correct - anyone who is interested can read the paper for themselves.

I believe it likely that the paper is correct, ethylmercury acts differently in the body and is safer than methylmercury. The available evidence does not support the idea that thimerosal alone can cause autism.

However, at the same time, I don't think that the case is completely closed. There are still unanswered questions and concerns that have not yet been addressed.

First, even though it was recommended in 2001 that thimerosal be removed from vaccinations, the existing stock of vaccinations were not recalled so were likely still used until exhausted. This means that the exact removal date isn't know and that some children could have been still receiving these vaccinations in 2002 and maybe even early 2003.

Second, thimerosal is still used in some vaccinations, such as certain versions of the flu shot, so it has not been completely removed. If you consider recent developments such as the swine flu shot, you will see it is still possible for a young child to get a sizable dose thimerosal (100 mcg over 30 days).

Third, it is not enough to say that thimerosal is not as bad as another form of mercury. It is still a form of mercury that has never had adequate safety testing (thimerosal vs placebo). It should be completely removed from vaccines as it is still a toxic substance and there are safer alternatives available.

Fourth, we don't yet have accurate data to tell us what is going on with the rate of autism in children born after thimerosal was removed. The normal figures the CDC publishes looks at the prevalence of autism in 8 year old children. This age was selected because it is thought that most children will be identified by this age and that the diagnosis is stable at this point.

The latest data available from the CDC is for children who were 8 in 2002. So to be able to do an apples to apples comparison we are going to have to look at children who are 8 and have never received thimerosal. If you look back to my first point, the first year we will be able to do this is 2009 (children born in 2001) although to be completely sure we will have to wait until 2011 or 2012 (children born in 2003 and later). At the rate the CDC is publishing data we won't have enough information for another 6 years.

Lastly, and most importantly, this research is talking about only one of the potential issues with vaccinations - thimerosal. Even if you accept the fact that is isn't likely that thimerosal alone causes autism that does not automatically say that vaccines in general are safe or that there aren't other potential problems.

The bottom line is that there is still a lot of research to be done and until that research is done the autism vaccine wars will continue.

1 comment:

  1. A reasonable thoughtful argument. If you come across any such studies, I'd love to know.