Leading the charge to protect thimerosal – also known as thiomersal — was the World Health Organization, or WHO, which coordinates global vaccination programs. “The fundamental position of WHO is that thiomersal vaccines are safe and effective and in fact essential products for protecting the majority of the world’s children and infants,” Dr. David Wood, an official in WHO’s Department of Immunization, Vaccines and Biologicals, told FairWarning.

Although thimerosal has been in use for seven decades, it no longer is in most children’s vaccines in the U.S. or other industrial nations. The change occurred in the U.S. after news broke in 1999 that the total dose of mercury received by infants who got all of their shots on schedule could exceed Environmental Protection Agency safety guidelines. However, that standard was based on methylmercury, the mercury that people are typically exposed to by eating contaminated seafood, not ethylmercury, the form in thimerosal. There still are no EPA safety guidelines specifically for ethylmercury.

Nevertheless, the revelation sparked a public furor. The American Academy of Pediatrics and the U.S. Public Health Service issued a joint statement announcing that although there was no evidence of harm, as a precaution they were asking manufacturers to eliminate the mercury content.

The academy, the nation’s dominant pediatricians group, highlighted the concerns in a 2001 report: “Mercury in all of its forms is toxic to the fetus and children, and efforts should be made to reduce exposure to the extent possible to pregnant women and children as well as the general population.”

The thimerosal was removed mainly by switching to single-dose vaccine vials that do not require a preservative. Today, American children under age six are routinely exposed to thimerosal only in some influenza vaccines, though trace amounts occur in one formulation of the combined diphtheria, tetanus, and pertussis vaccine.

Scientists have scrambled to determine how toxic ethylmercury is in the amounts included in vaccines. Recent epidemiological studies have failed to show a link between thimerosal and autism or other neurological problems – though thimerosal critics, citing some biological research, say they are not convinced. Still, leading authorities say the epidemiological studies along with findings that the body excretes ethylmercury much faster than methylmercury show that the preservative is safe.

“In contrast to 1999, there’s been an awful lot of work done in many different directions to look for harm from these thimerosal-containing vaccines, and we don’t seem to be able to find it,” said Dr. Louis Cooper, past president of the American Academy of Pediatrics.

Cooper co-authored a sharply worded commentary explaining the academy’s change of heart on thimerosal in an issue of its journal, Pediatrics, published in December, a month before the final treaty negotiations. “We balanced [the] known importance of thimerosal-containing vaccines to our global efforts to eradicate or eliminate these diseases, versus an absolute absence of a smoking gun to suggest that thimerosal is harmful,” he told FairWarning.

Nevertheless, Cooper points out that scientifically it’s very hard to prove a negative—in this case that a substance like thimerosal does not cause problems. And a belief that vaccines, and thimerosal in particular, cause autism continues to simmer in some pockets of the American public.

Protecting the poorest

For economic reasons, most developing nations use vaccines packaged in vials that contain two to 20 doses. These multi-dose vials are significantly cheaper—first, because of bulk pricing of the vaccine  and, second, because they occupy considerably less space per dose, the costs of refrigerating, storing, and transporting them are lower.

The trade-off is that they require a preservative to prevent the growth of contaminants accidentally introduced by the syringes inserted, one after another, into the vials. And thimerosal, the WHO says, is the most effective and safest known preservative. Vaccines with thimerosal are administered in more than 120 countries, to at least 64 percent of the world’s babies and children, according to WHO. In 2010 these vaccines prevented at least 1.4 million children from dying, the agency asserts.

A WHO study that examined eliminating thimerosal from vaccines concluded that switching to single-dose vials would be the best alternative. However, it  would increase the annual purchase cost of the most important children’s vaccines procured by UNICEF and WHO’s Pan American Health Organization by up to $333 million, equivalent to 64 percent of the agencies’ 2011 budgets for the shots. (The study estimated that the two UN agencies buy 30 percent of those vaccines globally.)

What’s more, the WHO report found that there would be substantial additional expenses to transport, refrigerate and store the single-dose vials, along with further burdens for manufacturers. The report concluded it would take 10 years or more to transition away from thimerosal.

The extra costs look modest compared to the more than $4 billion that the U.S. Centers for Disease Control and Prevention spent in 2012 to immunize poor children.

Yet considering that immunization programs in the developing world are stretched thin and underfunded even as 1.5 million young children die from vaccine-preventable diseases each year, the additional burden would hurt the world’s poorest, most vulnerable kids, said Michel Zaffran, coordinator of WHO’s Expanded Programme on Immunization.  Removing thimerosal “is not impossible. Of course everything is possible with time, with more resources, with more advocacy,” Zaffran said. “But if it is too sudden, then the disruption of the global immunization program would be tremendous.”

Still, Zaffran said his personal belief is that in the long run, eliminating preservatives from vaccines is desirable. He pointed out that any preservative carries certain risks, whether it’s added to drugs or food. They are, after all, designed to kill microorganisms.

The treaty is called the Minamata Convention on Mercury, after a Japanese city where industrial mercury pollution during the 1950s and 1960s killed or injured thousands of people. The treaty focuses on reducing mercury emissions from sources such as gold mining and coal-fired power plants, the biggest mercury polluters of air and water, according to the United Nations Environment Programme, the treaty coordinator. The treaty also bans mercury in a variety of products, including batteries, thermometers, certain fluorescent lamps, soaps and cosmetics, effective in 2020.

Unjust double standard?

Delegates hashed out the treaty language in five negotiating sessions that took place between June, 2010 and the final session in January, in Geneva. Voting delegates came from national governments, but civil-society organizations could provide testimony and lobby delegates.

Two American groups, veterans of the vaccine–autism wars at home, raised the issue of thimerosal during the rounds of negotiations. Representatives of California-based SafeMinds and Maryland-based Coalition for Mercury-free Drugs argued that the treaty should eliminate thimerosal-containing vaccines because they pose a serious health risk and alternatives are available. The groups contended that using vaccinations in poor countries that rich countries have abandoned constitutes an unjust double standard.

Eric Uram, SafeMinds’ executive director, said in an interview that questions remain about thimerosal’s safety for certain individuals, like babies with low birth weights or children exposed to mercury from other sources. Public health authorities, Uram said, “have been sold on the 50,000-foot view on this, that the benefits outweigh the risks. And the individual is excluded in that sort of an approach.”

Individual delegates from several countries expressed support for eliminating thimerosal either in public or private, Uram said. According to an official account, a delegate speaking on behalf of African nations made a public statement in favor of phasing out thimerosal during one meeting’s opening plenary session. And a group of unnamed countries  got a footnote advocating that thimerosal be phased down into a treaty draft. (The footnote was later removed.)

The WHO and other public health organizations mounted their own lobbying effort, and prevailed. The final treaty language, approved by consensus among all voting countries, excludes thimerosal and a mixed bag of other specialized mercury products from regulation. It also ensures that the issue is very unlikely to be reopened in the future.

“It was an emotive issue that kept on surfacing during the course of negotiations,” said the WHO’s Wood, who attended the last three negotiating sessions to make the organization’s case on the thimerosal issue. “It really wasn’t until the very last meeting that it became clear that the countries were very, very strongly in favor of ensuring that there was continued access to the thiomersal-containing vaccines.”

For his part, Uram chalks up his group’s defeat to countries being too beholden to WHO for funding, assistance and expertise to oppose the organization’s wishes. “We had no resources other than knowledge to try and overcome the financial and other obligations that WHO can provide,” Uram said.

Peter Ayuk Enoh, a delegate from Cameroon, said he joined other African nations that expressed concern about thimerosal during the negotiations, wondering why the preservative should still be used in Africa and elsewhere if it had been largely phased out in the U.S. and Europe. Ultimately, however, Enoh said they were convinced that the benefits of vaccination outweigh any risks from thimerosal, but pressed for more research to verify the preservative’s safety in the long term, or to find a substitute. “We had to compromise because we didn’t have any scientific proof that the administration of vaccines had any side effects,” Enoh said.

Some groups that advocated fiercely for more stringent terms during the negotiations and criticized the final treaty as not going far enough remained silent when it came to thimerosal. One was Bender’s coalition, the Zero Mercury Working Group. Bender explained that the treaty was aimed at reducing environmental contamination from mercury, particularly pollution that travels between continents, since no single country can solve the problem alone. One example would be emissions from Asian coal plants that ride the winds to North America.

So when Bender and his colleagues advocated for the treaty to eliminate mercury in dental fillings, they succeeded not by calling attention to  controversial health concerns but to the air and water pollution they cause (including when people with such fillings are cremated).

No such case could be made for thimerosal, Bender said. The amount of mercury released to the atmosphere from all human sources is estimated at 1,960 metric tons for 2010, but just 1.2 metric tons was used in thimerosal in 2011 according to the WHO report—a comparatively small amount.

In a rare area of agreement, both sides of the thimerosal debate are looking to new ways of delivering vaccines that don’t need a preservative but remain affordable for developing nations. These could include new devices like patches or nasal sprays, single-dose vaccines that require little or no refrigeration, or more efficient refrigeration and transportation technologies. Some new vaccines are already being developed along these lines, but achieving a global transformation could take decades, Zaffran said.

That change can’t come fast enough for Dr. Rozina Mistry. Until a year ago, she helped manage a program that delivers immunization and other health care throughout much of Pakistan, including to rural villages in the mountainous north. Child deaths from vaccine-preventable diseases have gone way down as a result of vaccinations, she said, but delivering them is arduous. Regular blackouts threaten the program’s refrigerated vaccine storage facilities. Some villages are accessible only by drives of up to 24 hours over rutted dirt roads that wear out 4-wheel drive vehicles in just a couple of years.

As it is, keeping vaccines cold is a huge challenge both logistically and financially, Mistry said, but switching to bulky single-dose vials “would mean that our ability to reach out, to store vaccines, and to actually run this program would be severely compromised, frankly speaking.” Until new ways to ease the cold-storage burden become available, she said, Pakistan and other developing nations will remain dependent on multi-dose vials containing thimerosal, if they want to keep their citizens immunized.