A global ban on thiomersal in vaccine manufacturing: stick with the science

(If you're not yet a fan, join us now by clicking the Like button)

Government representatives are meeting in Geneva this week to decide whether to introduce a global ban on mercury that could include thiomersal, a mercury-based preservative that has been used in some vaccine manufacturing since the 1930s to prevent bacterial or fungal contamination of multidose vials of vaccine.

Hosted by the United Nations Environment Program, the intergovernmental negotiating committee is charged with drafting a global treaty to rid the world of the threats posed by mercury.

Despite the ominous connotations of mercury, the decision should in theory be a no-brainer: The scientific and medical consensus is that thiomersal poses no human health risk, and that rather than saving lives, a ban would put millions of the world’s poorest children at risk of deadly diseases by disrupting vaccination programs.

But with vaccines, logic and evidence don’t always prevail. In the late 1990s we were at a similar juncture when, as part of a broader remit to find ways to reduce the human health hazards posed by mercury and under pressure from anti-vaccine lobbyists, the U.S. Food and Drug Administration turned its attention to the safety of thiomersal (known in the U.S. as thimerosal).

Despite a lack of evidence that it was harmful — and in the absence of any evidence to show that it wasn’t — the F.D.A. decided to take a precautionary approach and urged manufacturers to reduce or eliminate thiomersal from almost all vaccines in the United States.

Since then, scientists have published unequivocal evidence of its safety, including a 2006 study which showed that thiomersal is broken down by the body into ethylmercury. Unlike methylmercury, say from contaminated fish, which can make its way through the food chain and accumulate in the body, ethylmercury is naturally flushed out of the body within a couple of weeks. Despite such clinical and laboratory evidence, the damage to thiomersal’s reputation had already been done, and anti-vaccine campaigners are still trying to fan the flames.

Anti-vaccination groups have long campaigned against the use of thiomersal, claiming that this organic mercury derivative was responsible for increases in developmental disorders such as autism. What’s more, they argue that with a precautionary reduction already in place in the United States, denying children in developing countries access to the same thiomersal-free vaccines would be a global injustice.

Nothing could be further from the truth. Quite apart from the mountain of scientific evidence refuting any link between thiomersal and autism, with some studies involving hundreds of thousands of children, banning thiomersal or phasing out this agent would have a devastating impact on global health and lead to millions of children being denied access to life-saving vaccines.

To some extent, thiomersal is still used in vaccines in the United States and Europe, for example in some flu shots, but if there were a ban we could easily switch to single-dose vials.

In developing countries this is not so simple. Not only are single-dose vials less cost effective and less practical for mass vaccinations, they also take up more space in refrigerators, which are already at peak storage capacity. In the absence of any alternative preservative, far fewer vaccines would reach children in developing countries.

This would be a tragedy. In 2010 alone it is estimated that more than 1.4 million child deaths were prevented through the use of thiomersal-containing vaccines. Little wonder that organizations such as the World Health Organization, Doctors Without Borders, the American Academy of Pediatrics, the U.S. Institute of Medicine and the GAVI Alliance oppose a ban.

Indeed thiomersal is not the main target of the anti-mercury treaty, but rather an unfortunate bycatch. Even so, in many ways the situation mirrors the debate that took place more than a decade ago. This time it is the U.N.E.P. that is undertaking the laudable task of reducing the human health impact of mercury. The problem is that under pressure from anti-vaccine groups, hard scientific evidence is sometimes disregarded.

A recent example of this took place in December in a French case involving a claim by a former state employee that the aluminum content of vaccines given to him at work made him chronically ill. Although the court was not convinced of a probable link between the man’s illness and vaccinations, and in the absence of any scientific evidence of a link or any other explanation, it ruled in favor of the employee.

That is not to say that taking precautions isn’t intrinsically sensible; it’s just that sometimes dodging the issue in this way is not the best precaution, and instead of solving problems it sometimes creates them.

One of the core principles of medicine is “primum non nocere”: first, do no harm. But given the sheer numbers of lives at stake there is a strong argument that the burden of proof be shifted to the detractors.

Where a vaccine already has an established and strong safety record and is saving lives, the onus should be on producing evidence of a genuine risk before there is any change in policy related to its availability.

With millions of vulnerable lives at stake, the treaty negotiators need to engage and recognize that a ban on thiomersal would be bad policy based on bad science.

The New York Times (by Seth Berkley)

Comments are closed.