Experts Argue to Keep Thimerosal in Some Vaccines

The mercury component was removed from most childhood vaccines but doctors say an international ban would put more youngsters at risk of infectious diseases.

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The mercury component was removed from most childhood vaccines, but doctors say an international ban would put more youngsters at risk of infectious diseases.

The U.N. Environment Program is discussing ways to lower environmental exposure to mercury, a chemical linked to developmental problems. Part of the proposal involves removing thimerosal, a mercury-based compound used as a preservative to maintain vaccine quality, from immunizations given to children around the world.

The proposed ban could potentially create a situation in which thimerosal-containing immunizations, with their potential but still unknown health risks, are concentrated in lower-resource countries while developed nations rely on thimerosal-free shots, owing primarily to more robust health systems that allow better storage and preservation of the immunizations.

Adding to the growing controversy over the proposed policy, the American Academy of Pediatrics (AAP) endorsed a World Health Organization (WHO) recommendation to continue the use of thimerosal in vaccines. Since the 1930s, thimerosal has been used to prevent bacteria contamination of multidose vaccines like those against pertussis (whooping cough). In 1999, the AAP and the U.S. Public Health Service (USPHS) called for the removal of thimerosal amid concerns the compound was associated with higher rates of autism or other neurodevelopmental disorders. Flu vaccines are among the only shots given to children that still contain the mercury-based compound.

(MORE: How Safe Are Vaccines?)

However, in three papers published in the journal Pediatrics, a group of experts, including a former member of the AAP board of directors back in 1999, say there is now a lack of evidence that thimerosal causes these problems, and that the benefits of keeping thimerosal in vaccines to maintain their quality outweigh any potential health problems associated with exposure to small amount of mercury used. In the past 15 years, studies have found no significant harms linked to thimerosal, and in 2002 the AAP retired its original recommendation against it.

In the new statement, the AAP experts argue thimerosal should not be banned, noting that the preservative is critical for developing countries that rely on the chemical as an inexpensive method to preserve vaccines. Many vaccines are shipped in vials that contain more than one dose, to save on packaging costs. While these can be used to vaccinate more than one child at a time, multidose containers are also more prone to contamination, which is why they are often treated with thimerosal. In the U.S. and Europe, thimerosal has not been used for over 10 years because single-dose vials, which are more expensive to manufacture and which are disposed after they are opened, can be stored in refrigerators until they are needed. That’s not always possible in lower-resource countries, say experts, where many children remain unvaccinated against preventable diseases. Dr. Walter Orenstein of the Emory Vaccine Center at Emory University, an author of one of the papers, told NPR that without thimerosal, diseases like whooping cough could resurge in developing countries.

In addition, in assessing the benefits and risks of retaining thimerosal in vaccines, the WHO’s Strategic Advisory Group of Experts notes that there are no viable alternatives for the preservative and countries currently relying on thimerosal will simply lose their supplies of vaccines if a ban were approved. More children could contract the infections, putting their health at risk. “Global removal of thimerosal has the potential to adversely affect the worldwide vaccine supply,” the authors of one of the Pediatrics papers write.

Making vaccines without the compound could greatly hinder transportation and storage as well as create a spike in manufacturing costs. The WHO estimates it could cost two to five times more to produce vaccines without the mercury-based preservative.

(MORE: Vaccine Safety: New Report Finds Few Adverse Events Linked to Immunizations)

“The World Health Organization recommendation to delete the ban on thimerosal must be heeded or it will cause tremendous damage to current programs to protect all children from death and disability caused by vaccine-preventable diseases,” write two pediatric experts in one of the editorials.

They point out that the removal of thimerosal a decade ago was more out of an abundance of caution than based on any hard evidence of the compound’s health harms. “We made a mistake in our country,” Dr. Paul Offit, chief of infectious diseases at the Children’s Hospital of Philadelphia and co-creator of the rotavirus vaccine said to HealthDay of the removal of thimerosal. “To make the same mistake now, with the information we have now, it could result in thousands of deaths.” They also say that not all forms of mercury have the same effect on the body, and that the U.S. Environmental Protection Agency’s warnings of health harms apply primarily to methyl mercury, which builds up in fish and can remain in the bodies of people who consume fish for long periods of time, causing damage to the central nervous system. Ethyl mercury, the form of mercury found in thimerosal, may be less toxic to people.

The U.N. group will make its decision in January.

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