Thiomersal as a vaccine preservative.

Thiomersal poses a theoretical low risk of neurodevelopmental toxicity in infants. The known risk of morbidity and mortality from vaccine-preventable diseases and of contaminated multidose vaccine vials far outweigh any potential risk posed by thiomersal. However, with the weight of public opinion against the use of mercury of any sort, WHO and other agencies have begun the process of reducing and removing thiomersal from vaccines. In the short term (the next 3 years), modifications to existing strategies will result in a reduction in exposure to thiomersal. Over the long term (beyond 3 years), efforts will be focused on new vaccine-delivery technologies, alternative preservatives and combination vaccines, further reducing and eventually, perhaps, eliminating thiomersal from vaccines.