The World Health Organization is trying to fend off an effort to include a mercury derivative used in vaccines from being banned in a global treaty on mercury currently under negotiation.
The next round of talks for the proposed binding treaty begin on Oct. 31, and the Geneva-based UN health agency is trying to lobby for support of its position that banning thimerosal would be a mistake.
Thimerosal is a preservative used in many vaccines that are shipped to doctors and clinics in multi-dose vials.
Without a preservative, these vaccines would have to be produced in single dose formulations, which would drive up their cost considerably and create logistical problems, especially in developing countries.
David Wood, a WHO vaccines expert, said health ministries in participating countries may not have been aware of the fact that language that would ban thimerosal has been put into a draft treaty for the coming round of talks, which are being run by the UN Environment Program.
"Countries need to have their positions ready for that discussion," said Wood, co-ordinator of the quality, safety and standards team in WHO's immunizations, vaccines and biologicals department.
"That's part of our concern, that there could be decisions that are made that inadvertently could have a health impact. We just want to make sure that all of the relevant information and the facts are considered."
Tim Kasten, head of the UNEP's chemicals branch explained that the fact the language is in the draft doesn't mean it has the support of the majority of countries.
Anything proposed by any country is in the draft treaty — meaning, in fact that in some cases the document calls the same thing to be both banned and exempted. In the next and future negotiating rounds, countries will have to come to a consensus about what they want to remove and what they want to leave in, he said from Geneva.
"So there's a long road ahead yet on this. And most of the interest, shall I say, is coming from the NGO community on this one," Kasten said, referring to thimerosal.
Only countries can propose language for the treaty. But a number of non-governmental organizations — NGOs — are heavily involved in the discussions. Some are actively lobbying for the treaty to bar the use of thimerosal in vaccines and other pharmaceuticals.
Kasten said both the UNEP and the WHO believe other sources of mercury to be "more significant health threats" than thimerosal, though the final decisions are up to countries.
Negotiations aimed at limiting the risk from mercury began in 2009 after the UNEP's governing council decided voluntary efforts to reduce use and emissions of the chemical were not making a big enough impact.
What is envisaged here is a treaty, parts of which will be binding, with other parts voluntary.
There have been two negotiation sessions so far, with the third set to run from Oct. 31 to Nov. 4 in Nairobi, Kenya, home base of the UNEP. Two more will follow, with the treaty expected to be completed in 2013.
The WHO lists mercury as one of the top chemicals of public health concern in the world, a designation saved for the most hazardous of compounds. It is especially harmful for children and developing fetuses, with exposure leading to impaired cognitive development.
It is naturally occurring; volcanoes, for instance, emit mercury into the atmosphere. But most mercury is produced through the burning of coal and through industrial processes such as mining.
Despite its risks, it has long been used in a variety of products, including light bulbs, batteries and lamps. Mercury thermometers used to be standard, though newer thermometers don't use the chemical and the WHO is recommending the treaty urge that mercury thermometers no longer be used.
"There's growing momentum to phase them out," said Carolyn Vickers, the WHO's team leader for chemical safety.
Vaccines that contain thimerosal include those for influenza, rabies, and the triple shot that protects against diphtheria, tetanus and pertussis.
In some developed countries — Canada, the United States, the countries of Western Europe — thimerosal is no longer used in most pediatric vaccines. That shift was a response to concerns — since discounted — that with the high number of vaccines young children get, the cumulated exposure to thimerosal might pose a health risk.
Anti-vaccine activists also blamed thimerosal in childhood vaccines for rising levels of autism. But a Canadian study actually showed autism rates did not decline after thimerosal was removed from the vaccine formulations.
Canada has filed a position paper on the issue with the UNEP. While it says thimerosal will be phased out of vaccines used in Canada when safe alternatives are available, it believes there is no "legitimate safety reason to avoid the use of thimerosal-containing products for children or older individuals, including pregnant women."
The real impact of barring thimerosal use in vaccines would be felt in the developing world, the WHO and others said.
"The challenge in the rest of the world is that switching to single dose vaccines is going to make the logistics of vaccine delivery much more difficult," said Dr. Allison McGeer, an infectious diseases expert at Toronto's Mount Sinai Hospital.
"Most vaccines we have require a cold chain, so you have to keep them cold. That is already difficult to do in many countries. It's even more difficult to do if you increase the volume of the things you have to keep cold."
Single dose vials would be more expensive to produce and to transport because of additional packaging and bulk.
"For many vaccines and many countries, I don't think there's any doubt that that would compromise the delivery of all sorts of vaccines," McGeer said.