The American Academy of Pediatrics (AAP) today reiterated its concern that a proposed mercury ban by the United Nations Environmental Program (UNEP) could have devastating effects on the world’s most vulnerable children. The proposal includes a ban on thimerosal, a mercury-containing preservative used in vaccines in many developing countries.

The AAP and the World Health Organization said that the proposed ban would threaten access to vaccines for children in poor countries – where the risk from vaccine-preventable diseases remains high.

Ed Marcuse, MD, MPH, associate medical director for quality improvement at Seattle Children’s Hospital and member of the U.S. Food and Drug Administration’s Vaccines and Related Biologics Advisory Committee, said that the serious health risks that would result from a ban on thimerosal in vaccines far outweigh the potential environmental benefits.

“The proposed ban would have the potential to enormously increase the cost of vaccines, making them inaccessible to many of the world’s children,” says Marcuse.

Research shows no evidence of health risks from mercury in vaccines

In the late 1990s, thimerosal was removed from infant and preschool vaccines in the United States as a precaution following concerns about children’s exposure to any form of mercury. While methyl mercury is known to be harmful, little was known at that time about the risk of ethyl mercury, which is found in thimerosal. Since then, numerous studies have shown that there is no evidence of a health risk associated with thimerosal in vaccines.

“There is no credible scientific evidence that thimerosal in the concentrations in currently licensed vaccines is harmful,” says Marcuse. “Any risk to vaccinees receiving thimerosal-containing vaccines is unproven.”

Thimerosal helps prevent bacteria in vaccines

Thimerosal is still added to multi-dose vials of vaccines to prevent the growth of bacteria and fungi that could cause serious illness in vaccinees. Multi-dose vaccines are commonly used in developing countries because they are more affordable than the single-use vaccines typically used in the United States. Thimerosal-containing vaccines are also easier to use and transport in countries where refrigeration isn’t always available.

“Vaccine-preventable diseases continue to wreak havoc in many parts of the world, and their prevention is dependent on multi-use vials of vaccines,” says Marcuse. “Those multi-use vials rely on an anti-bacterial agent like thimerosal to ensure their sterility.”

Though the proposed ban wouldn’t have much effect on vaccines in the United States, Marcuse says the issue is a good reminder for parents to have a trusted pediatrician to rely on in the face of conflicting and confusing information.

“The science that underlies vaccinology is complex,” says Marcuse. “It’s not easy to sort through the conflicting opinions. You have to look very carefully at what the evidence base is.”

If you’d like to arrange an interview with Dr. Marcuse or another Seattle Children’s vaccine expert, please contact Children’s PR team at 206-987-4500 or


  • Centers for Disease Control and Prevention’s frequently asked questions about thimerosal:
  • World Health Organization Strategic Advisory Group of Experts’ recommendation on thimerosal-containing vaccines:
  • American Academy of Pediatrics’ statement about thimerosal-containing vaccines:
  • United Nations Environmental Program’s Intergovernmental Negotiating Committee – mercury proposal: