A prominent group of physicians and public health advocates argue that banning thimerosal, a mercury derivative, in vaccines could be a huge blow for vaccination efforts in low- and middle-income countries.

Thimerosal is used as a preservative in multi-dose vaccines in order to eliminate the threat of bacterial and fungal contamination. The United Nations Environmental Program is convening in a session next month in order to create a treaty banning certain processes and products. Mercury will likely be on the list and, physicians and public health experts fear, thimerosal will be included in that ban. Adding to the fear is that most of the voting ministers will be ministers of the environment, not of health.

In the United States, thimerosal is used only for a small portion of vaccines, namely certain types of flu shots. In the late 1990s, under a public concern about the link between thimerosal, vaccines, and autism, the American Academy of Pediatrics agreed that the preservative should no longer be used in vaccines. At the same time, the country, as well as other high-income countries, switched to single-dose vials for vaccines.

But now, the American Academy of Pediatrics says that they made that judgment under the medical ethical principle of "Do no harm". They say that there was very little research on the safety of the preservative. The link between autism and vaccines has been thoroughly debunked and no credible study has been found to prove that thimerosal is a threat, even though its cousin, methyl mercury, has been found to be.

Low- and middle-income countries bear most of the brunt of people dying from vaccine-preventable illnesses. Even now, multi-dose vaccines are difficult to administer to many people in these countries. Doctors argue that switching to single-dose vials would divert funds and attention away from the vaccinations themselves, and make the already daunting process of vaccinations even harder. They say that no viable alternative has been found for the preservative and that, if thimerosal is outlawed, it would make vaccines like tetanus toxoid, diphtheria-tetanus-whole cell pertussis, and hepatitis B all but outlawed as well.

Many advocates say that it is a travesty that the preservative is only used in developing nations and not developed ones. Indeed, doctors say that they will not be switching back to multi-dose vials in developed nations anytime soon. However, as Katherine King, Megan Paterson, and Shane Green write in a commentary in the journal Pediatrics, these advocates' concerns are misguided: "Treating individuals with equal regard, however, does not mean that all people are treated the same in all respects. Indeed, promoting equality in 1 sphere, such as health, often requires that people be treated differently in response to their unique needs and circumstances. It is only when differences in practice are not justified by differences in the needs and circumstances of the target individual or group, leading to avoidable harms, that concerns of injustice and inequality arise."

Other commentaries on the matter can be found in the journal Pediatrics.