- HICs —
- high-income countries
- LMICs —
- low- and middle-income countries
Thimerosal is an ethyl mercury–containing compound that has been used safely for >60 years as a preservative in multidose vials of vaccines to prevent bacterial and fungal contamination of those vials when they are repeatedly entered to withdraw doses.1,2 In the late 1990s, preservative-free single-dose vials were widely introduced into high-income countries (HICs). This was a precautionary move in response to theoretical concerns, now known to be unfounded, that ethyl mercury in thimerosal could build up in vaccine recipients’ bodies at a rate to similar methylmercury (a known toxin) causing toxicity.3 For low- and middle-income countries (LMICs), where the burdens of vaccine-preventable deaths are most profound, multidose vials of thimerosal-preserved vaccines are a critical part of immunization programs. Extensive additional resources associated with increased manufacturing, shipping, cold-chain storage, administration, and waste-handling infrastructure would be required by a move away from multidose vaccines; for example, a shift to single-dose vials would increase the annual cost of Pan American Health Organization– or UNICEF–supplied vaccines by >$300 million.4
In January 2013, governments are set to finalize the products and processes that will be prohibited in a multilateral environmental treaty, backed by the United Nations Environment Programme, which aims to restrict human and environmental exposure to mercury.5 As a mercury derivative, thimerosal could potentially be included within the treaty. Although supportive of the objectives of reducing human and environmental exposure to mercury, the World Health Organization’s Strategic Advisory Group of Experts on Immunization6 and much of the broader scientific and public health community7 have recommended that thimerosal be exempt from the treaty to avoid disruption to the global vaccine supply. In contrast, some nongovernmental organizations oppose such an exemption, arguing that it would be unjust to allow thimerosal to be used in LMICs when its use has been all but phased out of wealthier nations.8,9 This critique is misplaced. There is no injustice in allowing the use of thimerosal in vaccines. Rather, the real threat of injustice comes from considering the removal of this currently necessary and irreplaceable compound from the global vaccine supply, and the avoidable increases in morbidity and mortality that would inevitably result from disruptions to vaccination programs targeting already marginalized populations in LMICs.
Difference Does Not Signal Injustice
Although vaccines containing thimerosal are more widely used in LMICs than in HICs, a difference in immunization practice that would persist if thimerosal use were to continue in LMICs, the charge of injustice is misguided. Different practices, in and of themselves, do not make for injustice; they are morally problematic only if they are unjustified and compromise the interests of the affected parties. The moral intuition at work here is one of equality, that each life must be treated with equal respect and regard. 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. Thus, the use of thimerosal-containing vaccines in some jurisdictions but not others would only be unjust if this practice were harmful and unjustified. Neither is true.
There is no credible scientific evidence that the use of thimerosal in vaccines presents any risk to human health. Extensive pharmacologic and epidemiological research has shown early, theoretical concerns about links to autism or other neurodevelopmental disorders to be false.10–15 Indeed, the exculpatory strength of the data now available on thimerosal is well evidenced by recent statements from the Global Advisory Committee on Vaccine Safety,16 US Institute of Medicine,17 and American Academy of Pediatrics,18 all of which have concluded that thimerosal exposure through vaccination is not harmful to human health.
The Injustice of a Thimerosal Ban
In the absence of risk to human health, the use of thimerosal in vaccination programs in LMICs presents no threat of injustice. Rather, it is banning thimerosal that would cause an injustice to those living in LMICs and relying on these vaccines for effective protection against many harmful infectious diseases. Currently, multidose vaccines containing thimerosal are used in >120 countries to immunize ∼84 million children every year,19 saving the lives of ∼1.4 million people annually.20 They are also used throughout the world, including the United States and other HICs, for pandemic influenza vaccines, because it allows for more rapid production and easier dissemination of the vaccines.20 And yet, banning thimerosal would amount to banning such multidose vaccines, including tetanus toxoid, diphtheria-tetanus-whole cell pertussis, and hepatitis B vaccines.
After rigorous review by health regulators of its safety and efficacy, thimerosal, in accordance with World Health Organization standards, is approved for use in multidose vials of vaccines. Although there are other preservatives on the market, none are yet viable alternatives to thimerosal.21,22 In addition, substituting other yet-to-be-developed preservatives for thimerosal has the potential to alter vaccine stability, safety, and efficacy, and would require resource-intensive and time-consuming reformulation and testing of the vaccines.23 Complying with a thimerosal ban, then, would require all countries party to the treaty to exclusively use single-dose vials of vaccines, which would result in enormous strain on the resources and public health infrastructure of many LMICs.24 Even if cost and distribution challenges could be met in at least some LMICs, it is projected that countries would face interruptions to vaccine supply, particularly for the most basic, routine vaccines.20 The result would be millions of people, predominately in LMICs, with significantly restricted access to lifesaving vaccines for many years.
Not surprisingly, during the course of negotiations, LMIC governments have questioned whether thimerosal should be exempted from the treaty.25 The resistance to its continued use comes entirely from nongovernmental organizations in HICs, the populations of which would not suffer the consequences of the potential ban. Where’s the justice in that?
We thank Billie-Jo Hardy, Jocalyn Clark, David Wood, and Walt Orenstein for helpful discussions and/or for their comments on earlier versions of this article.
- Accepted October 15, 2012.
- Address correspondence to Shane K. Green, PhD, Sandra Rotman Centre, MaRS Building, South Tower, 101 College St, Suite 406, Toronto, ON, Canada, M5G1L7. E-mail:
Dr King conceptualized the paper, contributed to drafting the manuscript, and approved the final manuscript as submitted; M. Paterson performed the initial research and analysis, contributed to drafting the manuscript, and approved the final manuscript as submitted; and Dr Green conceptualized the paper, contributed to drafting the manuscript, and approved the final manuscript as submitted.
Opinions expressed in these commentaries are those of the authors and not necessarily those of the American Academy of Pediatrics or its Committees.
FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.
FUNDING: The authors are members of the Ethical, Social, and Cultural (ESC) Program for Global Health, which receives funding from the Bill & Melinda Gates Foundation, a founding partner of the GAVI Alliance.
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- ↵US Food and Drug Administration. Vaccines, Blood and Biologics: Thimerosal in Vaccines Questions and Answers. US Department of Health and Human Services. Available at: www.fda.gov/BiologicsBloodVaccines/Vaccines/QuestionsaboutVaccines/UCM070430 Published April 30, 2009. Accessed September 25, 2012
- ↵American Academy of Pediatrics and US Public Health Service. Joint statement of the American Academy of Pediatrics (AAP) and the United States Public Health Service (USPHS). Pediatrics. 1999;104(3 pt 1):568–569
- ↵World Health Organization. World Health Organization Immunizations, Vaccines and Biological, Immunization Practices Advisory Committee (IPAC). Final Meeting Report and Recommendations, April 17–18, 2012. Available at: www.who.int/immunization_delivery/systems_policy/IPAC_2012_April_report.pdf. Accessed September 25, 2012
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- ↵Ban on all mercury-based products would risk global immunization efforts, says AAP, WHO. AAP News. June 1, 2012. Available at: http://aapnews.aappublications.org/content/early/2012/06/01/aapnews.20120601-1.full?rss=1 Accessed September 25, 2012
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- Copyright © 2013 by the American Academy of Pediatrics