Thiomersal in vaccines: is removal warranted?

The mercury-based vaccine preservative thiomersal has come under scrutiny in recent months because of its presence in certain vaccines that provide the foundation of childhood immunisation schedules. Over the past decade new vaccines have been added to the recommended childhood schedule, and the relatively smaller bodyweight of infants has led to concern that the cumulative exposure of mercury from infant vaccines may exceed certain guidelines for the human consumption of mercury. In the US, government agencies and professional societies have recently recommended that thiomersal be removed altogether from vaccines. Some involved in developing vaccine policy feel that the evidence to support these safety concerns has not risen to the level required for such a response. This apparent divergence of opinion has left healthcare professionals and the public with uncertainty about the potential health effects from low level exposure to thiomersal as well as the necessity of removing thiomersal from vaccines. At present, scientific investigation has not found conclusive evidence of harm from thiomersal in vaccines. As a precautionary measure, efforts are under way to remove or replace thiomersal from vaccines and providers should anticipate the availability of more vaccine products that are thiomersal-free over the coming years.