Global vaccination recommendations and thimerosal.

Vaccines remain one of the most effective ways to prevent infectious disease and deaths globally. Universal childhood immunization provides herd immunity against many infectious agents and is a policy that has achieved dramatic reductions in common childhood illnesses. Thimerosal, which contains ethyl mercury, has been used as a preservative in vaccines to prevent contamination of multidose vials from bacteria and fungi since the 1930s. Although there are clear neurotoxic effects of methyl mercury absorption, ethyl mercury has not been associated with those consequences. Nevertheless, before data were available on risks of thimerosal in vaccines, in 1999 the American Academy of Pediatrics and the US Public Health Service recommended moving toward removing thimerosal use in preservatives as a precautionary measure. Thus, thimerosal as a preservative has been removed from most vaccines in the United States, generally resulting in distribution of vaccines in single-dose rather than multidose vials. US vaccines routinely recommended for children that still contain thimerosal as a preservative are seasonal influenza vaccines including the multi-dose presentation Afluria (CSL Limited) and multidose formulations (Fluzone (Sanofi Pasteur) and Fluvirin (Novartis). Thimerosal remains an important vaccine preservative in resource-poor countries. Thimerosal allows the use of multiuse vials, which reduce vaccine cost and the demand on already constrained cold-chain systems. Even in the United States, thimerosal could be critical for dealing with emergencies and the need to rapidly increase vaccine supply and delivery, such as during a serious pandemic of influenza.