The Hannah Poling matter: A tale of science, belief and ‘plausibility’

The ongoing controversy about childhood immunizations and autism is not a matter that comes up every day in the life of an adult infectious disease physician. Because of the increasing public concerns, however, adult infectious disease physicians may well be questioned about it by parents, other members of the public, the media and the like. It is well, therefore, to be cognizant of the issues and to be aware of the facts when the inevitable questions arise.

In August 2007, I outlined in this column the nature of the nine test cases representing the almost 5,000 cases of alleged vaccine-related autism brought before the special masters of the U.S. Court of Federal Claims, tried under the Vaccine Injury Compensation Program.

Initially, the standard used by the Court to assess causation was “a preponderance of evidence.” Using that standard, scientific evidence was generally held in higher regard than testimonial evidence, even though the argument for vaccine-related injury might appear to be plausible. Several years ago, however, the Court changed the standard used to one simply of “plausibility.” Using that standard, the Court might rule that a particular injury case was vaccine-related if a plausible biological argument could be made that the injury might have been caused by a vaccine, even though researchers of sound epidemiologic studies identified no evidence of such a relationship.

Hannah Poling

The Hannah Poling story is a dramatic example of the Court’s application of the “plausibility” standard. Hannah is the daughter of Jon and Terry Poling. In 2000, Jon was a neurology resident at Johns Hopkins Hospital, and Terry was a registered nurse as well as a lawyer. In 2000, Hannah was 19 months old, with normal growth and development to that time. Because of intercurrent illnesses, some immunizations had been delayed and in July, she was given five vaccines against nine specific vaccine-preventable infections. Shortly thereafter, her central nervous system deterioration began, and she was ultimately diagnosed as having autism spectrum disorder. Further complicating her case was the fact that she was also found to have a mitochondrial disorder and that this was believed to have contributed to the development of autism. The Polings’ expert testified in court that the five vaccines administered had “stressed” her already weakened system and worsened her developing autism. The court was persuaded, without even holding a hearing, that the claim was biologically plausible and ruled in the Poling family’s favor. Damages have not yet been determined.

For many who are hesitant about giving their children recommended vaccines, this ruling is seen as an admission by the U.S. government that vaccines may cause autism. Not so, claimed the CDC. “Let me be very clear that the government has made absolutely no statement indicating that vaccines are a cause of autism,” said Julie Gerberding, MD, MPH, CDC director. “That is a complete mischaracterization of the findings of the case and a complete mischaracterization of any of the science that we have at our disposal today.”

This ruling took the experts on mitochondrial disease totally by surprise, because they are not aware of any scientific basis to believe that mitochondrial disorder is exacerbated by vaccines. Indeed, one expert at Columbia University suggested that such people, who may be especially susceptible to infections, are even more likely to benefit from vaccines.

Unique case

Medicolegal experts have indicated that the wording of the ruling is quite narrow and the circumstances quite unique; thus, the Poling case is not likely to be a precedent for the many other pending claims. Nonetheless, it is the first crack in the otherwise ironclad government claim that vaccines do not cause autism. Each case in the future will need to be decided on its own merits. Note also that the ruling did not address what vaccine or what additive, ie, thimerosal, was the villain in this case; it shed no further light on that ongoing controversy. Nonetheless, it is widely believed among the vaccine skeptics that thimerosal is indeed the cause of autism.

An enormous amount of ink has been spilled concerning this issue in the public media in the two months since this ruling was released. It is clear that virtually all the vaccine skeptics in the country believe they have won a victory and that the government has either been lying to them or else really does not know the full extent of possible damages that vaccines (or thimerosal) may cause. Consider the following statement from the CDC issued in response to concerns about thimerosal:

“CDC places a high priority on vaccine safety and the integrity and credibility of its vaccine safety research. This commitment not only stems from our scientific and medical dedication, it is also personal, for most of us who work at CDC are also parents and grandparents. And as such, we too have high levels of personal interest and concern in the health and safety of children, families and communities. We simply don’t know what causes most cases of autism, but we’re doing everything we can to find out. The vast majority of science to date does not support an association between thimerosal in vaccines and autism. But we are currently conducting additional studies to further determine what role, if any, thimerosal in vaccines may play in the development of autism. It is important to remember vaccines protect and save lives. Vaccines protect infants, children and adults from the unnecessary harm and premature death caused by vaccine-preventable diseases.”

Note the ambiguities in that statement. No wonder a skeptical public might believe that vaccines are not as safe as the CDC has been telling us, many scientific studies notwithstanding. As pointed out by Rahul Parikh, MD (Pediatrics. 2008;121:621-622), this is a great example of why we are doing so poorly in risk communication.

Public health implications

The public health implications of the Poling ruling are worrisome, but it is far too early to assess the possible damage. Most state immunization regulations permit exemptions for personal beliefs or religious reasons. These exemptions have already resulted in pockets of susceptible populations that have resulted in small epidemics of several diseases in the past. If the proportion of exempted children now increases significantly, there would be real cause for concern.

One of the fundamental laws of logic is that one cannot prove a universal negative, and in the final analysis, this is the ultimate Achilles’ heel in the many excellent epidemiologic studies of vaccine safety. Why the court changed its standard from “a preponderance of evidence” to mere “plausibility” is unknown to me (though it would certainly be interesting to find out), but the Poling case is a vivid example of the mischief that using that standard can create.