Pediatricians React to Proposal to Ban Thimerosal in Vaccines

thimerosal, vaccines, immunizations, global health

Physicians and public health experts are joining together to oppose a request by the United Nations Environment Program (UNEP) that thimerosal, a mercury-based preservative, be removed from vaccines because of concerns regarding its potential neurotoxic effects. The ingredient is rarely used any longer in the United States; however, in developing countries making such a change may put immunization programs under financial duress, thus causing a public health issue, says the World Health Organization.

Thimerosal is used to prevent the growth of bacteria and fungi in multi-dose vials of vaccines. Because the preservative contains mercury (in the form of organic ethyl mercury), concerns were raised about children, with the many vaccines recommended in early childhood, would exceed the safety threshold set by the US Environmental Protection agency based on studies of inorganic methyl mercury.

Although at the time there were no studies regarding the potential harm of ethyl mercury and the amount of mercury children would receive would not rise above thresholds set by other agencies, such as the Agency for Toxic Substance Disease Registry and the FDA, thimerosal was eventually removed from vaccines in the United States. Today, most vaccines – with the exception of certain types of flu shots and in some adult vaccines - are given from single-dose vials thus eliminating the need for thimerosal.

However, in countries with fewer resources – where children still die from vaccine-preventable diseases - thimerosal is still widely used. It is cheaper and easier to use multi-dose vials of vaccines against diseases such as diphtheria and tetanus, for example.


The World Health Organization’s Strategic Advisory Group of Experts (SAGE) notes that there are no viable alternatives to thimerosal and that replacement with an alternative preservative may affect the quality, safety and efficacy of vaccines.

Banning the preservative may also harm the world’s vaccine supply by increasing manufacturing costs (researchers estimate it could cost anywhere from two to five times as much to manufacture thimerosal free-vaccines), reducing manufacturing capacity, increase waste from single-dose packaging and strain transportation and storage space, says Walter Orenstein, MD, of Emory University in Atlanta, a member of the AAP Committee on Infectious Diseases.

Reducing mercury exposure "is a wonderful thing," Orenstein said. However, "We need this exception because thimerosal is so vital for protecting children. The continued benefits of thimerosal use in vaccine manufacturing clearly outweigh any perceived risks," he concludes.

The American Academy of Pediatrics, the Pediatrics Infectious Diseases Society, and the International Pediatric Association all support WHO in stating that "it is essential that access to thimerosal-containing vaccines is not restricted under this global initiative (to reduce environmental mercury)."

The United Nations Environmental Program is convening in a session next month in order to create a treaty banning certain processes and products thought to be “global health hazards” with mercury likely to be on that list.

Source references:
Cooper L, Katz S. "Ban on thimerosal in draft treaty on mercury: why the AAP's position in 2012 is so important"Pediatrics 2013;131:152-153.
AAP. "Statement of endorsement: recommendation of WHO Strategic Advisory Group of Experts (SAGE) on immunization" Pediatrics 2012.
King K, et al. "Global justice and the proposed ban on thimerosal-containing vaccines" Pediatrics 2013;131:154-156.