Mercury heats up

January 2003

---Philip A. Brunell, MD

I usually learn a lot at holiday time about what people are thinking when they do not encounter me as a physician. I got an earful this year about thimerosal. It was not too surprising that some of these very intelligent people had concluded that thimerosal caused autism. This comes under the category of “if you repeat something often enough, people will believe it”. The lay press has been full of it (you can interpret this any way you like). I reminded some of the people with whom I spoke that whole cell pretties vaccine was said to cause sudden infant death and infantile spasms until carefully done studies exonerated the vaccine on both counts. I have a wonderful photo in my slide collection of an infant who was admitted to our service in the throes of an “infantile spasm” and his EEG with showed a typical hypsarrhythmia pattern. This child had been admitted a couple of days prior to his appointment for his first DTPw. If he had had his DTPw two days earlier there is no way the parents could have been convinced that this was not the cause of the child’s condition. I must repeat that the plural of anecdote is not proof. Issues of this kind are settled on the basis of carefully done epidemiologic studies.

There are a number of things that have led to the assumption that autism was in deed caused by thimerosal. First, was the decision to remove thimerosal from vaccines. Many have interpreted this as an admission of guilt. Second was the Institute of Medicine (IOM) report, which did not exonerate thimerosal. Indeed, it stated that it was biologically plausible that the mercury in thimerosal might have caused brain injury. All of us who are familiar with the Mad Hatter in Alice in Wonderland can agree mercury may affect the brain. However there have been enough textbook descriptions of both acute and chronic mercury poisoning in children including Minamata Disease which affected the fetus, to make me wonder whether what has been alleged to be caused by thimerosal is consistent with mercury poisoning (see Nelson on mercury poisoning in children). Where are the other manifestations of mercury poisoning with which it has been associated, eg, renal damage, acrodynia or skin changes? In individuals poisoned with large quantities of organic mercury, the neurologic signs are not congruent with those of autism or ADD.

The IOM statement does not claim that thimerosal in childhood vaccines could cause brain damage. It is not a statement of fact. The IOM’s conclusion was that there was not enough evidence one way or another to make a judgement. This was one of the five options open to them. They simply could not conclude that it was or was not causally related. One of the problems the IOM committee faced was the dearth of information on the effect of ethylmercury on humans.

Mercury is a known neurotoxin. Little is known about ethylmercury (the active component in thimerosal) compared to methylmercury. The committee concludes that although the hypothesis that exposure to thimerosal-containing vaccines could be associated with neurodevelopmental disorders is not established and rests on indirect and incomplete information, primarily from analogies with methylmercury and levels of maximum mercury exposure from vaccines given in children, the hypothesis is biologically plausible. The committee also concludes that the evidence is inadequate to accept or reject a causal relationship between thimerosal exposures from childhood vaccines and the neurodevelopmental disorders of autism, ADHD, and speech or language delay. The limited and unpublished epidemiological data constitute weak and inconclusive evidence regarding causality.

Enter the lawyers. Although vaccine injury now is covered under the Vaccine Injury Compensation Program (VICP), they have found a way to circumvent this and go directly for the jugular. There are now billions of dollars of suits filed claiming that mercury in not a component of the vaccines, and thus covered under VICP, but that it is a contaminant. This is being challenged in court by the government. The amount of the pending suits is estimated to be several time the gross receipts from the sale of vaccines globally. This is not a situation, which will encourage vaccine manufacturers to stay in this business.

Enter the congress. Tucked away in the Homeland Security Bill was a portion exempting manufacturers from being sued for thimerosal in vaccines. No one quite knows why or how this got into this bill but you can bet there is lots of conjecture. Apparently it was lifted from some other legislation authored by retiring Rep. Dick Armey (R-Texas). In a flood of letters to the New York Times (of which one appeared to be authored by a drug manufacturer representative), it was claimed appropriate to have this provision in this legislation. It went on to state that vaccines against bioterrorism might need to contain thimerosal, giving smallpox as its example. Parenthetically, putting mercury in smallpox vaccine would inactivate it. The medical department obviously did not clear this letter. Parents who believe their children were affected by thimerosal are upset both because of the way this was enacted but also because the statute of limitations on the VICP has expired for many of the plaintiffs. Efforts are being made to address the latter.

Enter some science. In The Lancet (November 2002) there is an article demonstrating slower clearance of methyl as compared ethyl mercury. Only about two-thirds of the 2- or 6-month-olds immunized with DTPa, HepB and Hib simultaneously containing thimerosal had blood mercury levels detectable by the assay used. The levels of the others were far below those associated with methylmercury levels in cord blood, which were related to subtle neurologic defects in prior studies. What the study does not answer is how much of the ethylmercury disappeared in nervous tissue. Ethylmercury appears to be converted more rapidly than methylmercury.

The most useful information will probably come from the analysis of the data that have been collected on American children. Although the initial analysis of these data suggested a slightly increased risk of some neurologic problems in children receiving mercury-containing vaccines, reanalysis has essentially wiped out these differences. At the present time, I know of no case of brain damage that was proven to be caused by thimerosal in routinely used vaccines. In any case, all vaccines now are available free of thimerosal with the exception of traces that remain in a few. For pregnant women who fear the effect of mercury on fetuses there is even influenza vaccine free of mercury. If they really want to be certain, they should avoid tuna and other mercury containing fish.

Conflicting claims on the effect of eating seafood, high in methylmercury, on the effect on the fetus. Apparently consuming fish in the Faroe Islands appears to have some effect as measured by neurodevelopmental testing, while Seychelles consumers appear to have improved function. Although the detrimental effect in the Faroe Islanders has been attributed to the polychlorinated biphenyls concentrated in the fat of consumed whale blubber, the authors of the article appear to have shown that this is not the case. Both these studies describe the effect of methylmercury on the fetus, neither of which is the issue (JAMA. 1998;280:737); Neurotoxicol Teratol. 1997;6:417). Thimerosal contains ethylmercury and it is given postnatal, not to fetuses.