succumbing to peer pressure

Wednesday, April 23, 2008

Vaccination Schmaccination

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.


Anonymous Anonymous said...

Agreed! Don't even get me started on media coverage of all things scientific...

3:32 PM  
Anonymous Anonymous said...

Maybe you should do a bit of research yourself. Hannah Poling's case is not unique. Check recent reports to see that it is being estimated that approximately 65% of children with autism have exactly the same problem.

5:54 PM  
Blogger Megan said...

I never said that she was unique - I said she had a very specific and rare underlying condition. Even if your claim that 65% of autistic children may have the same condition (something I find dubious since you fail to site a source), that would still account for a minority of all children. Hence, the risk for the average, healthy child, is still quite small.

I choose my words very carefully and try to be precise in what I say - it would be great if you could exercise such care in reading my words.

8:06 PM  
Blogger kevin said...

I wholeheartedly agree, and can only add that while it is indeed difficult to have a child with autism, it's also no dance around the maypole to have autism.

12:48 AM  
Anonymous john Howard said...

Additionally, are autism rates really "skyrocketing" or is it just being more frequently diagnosed?

Now let's talk about the "epidemic" of food allergies.

7:10 AM  
Blogger Megan said...

John Howard brings up an excellent point - there is a critical difference between diagnoses of an illness and actual cases of an illness. Since, barring omnipotence, we are only ever able to identify those with a certain diagnosis, many instances of 'increased prevalence' are actually the result of changes in our definitions of certain disorders. You see this a lot with ADHD and bipolar disorder - they have approximately 5 overlapping symptoms, so there are identifiable trends where cases of one will increase while cases of the other decrease, simply because the same individual with the same symptoms is being classified one way or the other depending on time period and, frequently, geographical location. I'm not as familiar with autism, but I have heard that people who are today classified as autistic may have historically been labeled with other types of behavior disorders.

Also, above, clearly, I mean 'cite,' not 'site.' That's karma biting me in the ass for being snarky.

8:40 AM  
Anonymous puzzled said...

A wonderfully clear and convincing post. However, your careful explanation of "failure to reject the null" language confirmed my view that classical statistics does not suit most people's cognitive style. We should all be Bayesians.


9:11 AM  
Anonymous puzzled said...

A wonderfully clear and convincing post. However, your careful explanation of "failure to reject the null" language confirmed my view that classical statistics does not suit most people's cognitive style. We should all be Bayesians.


9:12 AM  
Blogger Janice said...

The following quote is by Dr. Jon Poling, father to Hannah, practicing neurologist, and clincal assistant professor at the Medical College of Georgia:

"In the only population-based study of its kind, Portuguese researchers confirmed that at least 7.2 percent, and perhaps as many as 20 percent, of autistic children exhibit mitochondrial dysfunction. While we do not yet know a precise U.S. rate, 7.2 percent to 20 percent of children does not qualify as "rare." In fact, mitochondrial dysfunction may be the most common medical condition associated with autism. Although unlikely, if the Portuguese studies are incorrect and mitochondrial dysfunction were found to be a rarity occurring in less than 1 percent of all autism, it would still impact up to 10,000 children (250,000 worldwide), based on current estimates that 1 million people in the U.S. (25 million worldwide) have autism. If, on the other hand, the research showing that 7.2 percent to 20 percent of children with autism have mitochondrial dysfunction is correct, then the implications are both staggering and urgent."


5:08 PM  
Blogger Janice said...

"Even if your claim that 65% of autistic children may have the same condition (something I find dubious since you fail to site a source), that would still account for a minority of all children. Hence, the risk for the average, healthy child, is still quite small."

I find this kind of thinking very scary. This statistics game shouldn't be played when we're talking about the kind of injuries resulting from vaccines given to kids whose bodies can't handle them. My son is severely impaired from his autism - he's five years old and cannot speak a single word. He has no toileting skills, nor does he have any social skills. If no "cure" is found, he will not ever be independent. I think if the vaccine schedule poses significant risks for a subset of children, it is not an acceptable schedule. My wish is not that the vaccine program be scrapped, but that researchers identify the subsets of the population that would be at risk of damage so as to prevent damage from occuring. I agree that diagnosis of autism is increasing, but I feel that is corelating with the rise in the incidence of the disease. I have two autistic children, but no autistic relatives. That's not better diagnosis, it's diagnosing what's suddenly present and obvious to the common eye.


6:29 PM  
Blogger Megan said...

Janice - thanks for the reference. " least 7.2 percent, and perhaps as many as 20 percent, of autistic children" - the key phrase here is of autistic children. This particular mitochondrial disease may not be rare within the subpopulation that has autism, but it is rare among the general population.

Also, I never meant to imply that children who have been identified as at elevated risk for bad reactions to vaccines should be encouraged to play vaccine russian roulette (in fact, I'm fairly sure I specifically stated the opposite). Rather that if such a link is identified in a specific subset of the population, we should not infer that to mean that the general population is at an elevated risk or that a link exists for children absent this underlying disorder.

7:03 PM  
Blogger Janice said...

Rare in the general population? Let's not forget that most children on the autism spectrum were once part of the "general population". Let's think of it another way. If 250,000 children worldwide (I take that number from the quote I posted earlier) were turning bright purple, stinking of rotting fish and losing all of their hair in reaction to vaccines as a result of ANY underlying genetic anomaly that predisposed them to risk of injury from vaccines, do you think there would be any debate about whether 250,000 was a significant portion of the world population?

5:07 PM  
Blogger Megan said...

Janice - rare is a specific connotation in public health - a rare disease is defined by the National Institute of Health as anything that occurs in 200,000 individuals in the United States or fewer. So with the numbers you're citing it looks like this mitochondrial disorder may be on the bubble, but perhaps is not technically 'rare,' depending on how the statistics work out. However, I would like to point out that my use of the term is not to slight the impact of the disease - illnesses are not defined as rare because they are considered to be not a big deal, or to imply that the portion of the population they affect are somehow less important. Rather, it is a way to quantify the risk posed to the entire population (hence the word public at the beginning of public health).

As I believe we have both already agreed, if there is a way to identify children who are at added risk for negative reactions to vaccines, those children should probably not be exposed to vaccines (or should be offered an alternative schedule to give their bodies time to recover). Such a mechanism already exists in the medical community - as I stated in my original post, there are plenty of valid medical reasons for certain subsets of the population not to get vaccinated. The problem is when this specific set of information about a specific set of individuals is inaccurately generalized to apply to the public at large, which is what people repeatedly attempt to do in linking vaccines to autism. Such a link simply does not exist for the general public.

6:13 PM  
Anonymous A. Bunker said...

«"In the only population-based study of its kind, Portuguese researchers confirmed that at least 7.2 percent, and perhaps as many as 20 percent, of autistic children exhibit mitochondrial dysfunction.»

Your proof is a study by scientists working in some third world country?!

Give us a break and give us an example of a real study made in the USA.

4:43 AM  

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