Experts question proposed mercury preservative ban in vaccines

By Liam Davenport, medwireNews Reporter

A ban on the use of a mercury-based preservative in vaccines tabled by the United Nations Environmental Program (UNEP) should be struck from a draft treaty as it may severely affect access to vaccines, experts urge.

The American Academy of Pediatrics (AAP) has issued a statement underlining that the proposed outlawing of the use of thimerosal, which contains ethyl mercury, is based on outdated assumptions over the toxicity of the preservative. The statement echoes a recent World Health Organization (WHO) recommendation that the ban be removed from the UNEP treaty.

This is a reversal of the position taken by the AAP and US Public Health Service (USPHS) in 1999 to eliminate mercury from vaccines, following a review by the US Food and Drug Administration showing the cumulative amount of ethyl mercury in vaccines may exceed guidelines established for inorganic methyl mercury.

As a result, by 2001, mercury was removed from most vaccines in the USA and other countries, although thimerosal is still found in some seasonal influenza vaccines and some multidose formulations.

However, as Walter Orenstein (Emory University, Atlanta, Georgia, USA) and colleagues observe in the statement in Pediatrics: "These limits were based on methyl mercury's accumulation in the body due to its long half-life, which is ~7 times greater than that of ethyl mercury."

Evidence collected over the past 15 years shows there is no significant harm associated with the use of thimerosal in vaccines, they note, including serious neurodevelopmental disorders, a finding that has been borne out in dozens of studies from around the world.

"Had the evidence that is available now been available in 1999, the policy reducing thimerosal use would likely have not been implemented," Orenstein and colleagues comment.

The AAP statement emphasizes that thimerosal allows the use of multiuse vials, which reduces the cost of vaccines and the impact on already strained cold-chain systems. Its removal could therefore potentially adversely affect the worldwide supply of vaccines. Furthermore, the use of thimerosal could be critical for dealing with health emergencies in the USA, the authors say.

In an accompanying commentary, Louis Cooper (Columbia University, New York, USA) and Samuel Katz (Duke University, Durham, North Carolina, USA) who were involved in the original 1999 AAP recommendation, state: "The WHO 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."

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