This is a guest blog by Erin Fry, Government Affairs Officer of PATH.

The United Nations Environment Programme (UNEP) is supporting the development of a treaty on mercury which may include language that impacts access to vaccines in poor countries.

Thiomersal (which also goes by the name thimerosal) is a key preservative that contains small amounts of ethylmercury and is used in most multi-dose vaccines to prevent bacterial and fungal growth in vaccine vials. It can be found in vaccines for major killers of infants and children like tetanus and pertussis, as well as hepatitis B, rabies, influenza, and meningococcal diseases.

Although data from many studies show no convincing evidence of harm caused by the low doses of thiomersal in vaccines, the UNEP International Negotiating Committee (INC) has added pharmaceutical products, including vaccines, to a draft list of mercury-added products to be banned in its most recent draft.

Over the past ten years, reputable scientific bodies have evaluated the safety of thiomersal. The World Health Organization’s (WHO) Global Advisory Committee on Vaccine Safety concludes that existing thiomersal-containing vaccines are safe and that any risks are unproven. Similar conclusions have been drawn by the US Institute of Medicine, the American Academy of Pediatrics, the UK Committee on Safety of Medicines, and the European Medicines Agency.

The implications of restricting the manufacture, distribution, or use of thiomersal could significantly limit access to several lifesaving vaccines in poor countries. According to WHO, making vaccines thiomersal-free would require using either12:

  • an alternative preservative (which would require costly and time-consuming clinical studies, thereby driving up the cost of the vaccines); or
  • preservative-free single-dose vaccines exclusively (which would considerably increase costs and require twice the storage and transport capacity, an impossibility for most countries).

Neither of these scenarios is desirable, particularly given that there is no evidence to suggest that removing thiomersal from vaccines would result in a positive health impact.

The treaty is under the auspices of environmental entities, and the global health community is just beginning to engage. Civil society organizations are invited to formally submit comments to the UNEP; however, the majority of health-related comments submitted to date reflect inaccurate scientific information and suggest that thiomersal should not be used in vaccines.

It is critical that the global health community’s voice be heard in the upcoming negotiations and that access to life-saving vaccines not be limited by misinformation about thiomersal. Please contact Erin Fry at if you would like to get involved.