thimerosal

Thimerosal, also known as thiomersal, is an organomercury compound used primarily as a preservative in several vaccines and some ophthalmic and dermatologic products. It is a sodium ethylmercurithiosalicylate compound that helps prevent bacterial and fungal growth in multi-dose vials.

The compound has been used in vaccines since the early 20th century to extend shelf life and reduce contamination risk in multi-dose formats. It remains a widely used preservative in various pharmaceutical products in some countries, though formulations for many pediatric vaccines have been made thimerosal-free or reduced to trace amounts.

Safety and regulatory status have been the subject of extensive study. Numerous reviews and studies have found no convincing evidence that thimerosal at the levels used in vaccines causes autism, developmental delays, or other long-term adverse effects in children. In response to public concern, U.S. and international health authorities recommended reducing or eliminating thimerosal in vaccines given to young children while preserving vaccine safety. By the early 2000s, many vaccines in the United States were reformulated to be free of thimerosal or to contain only trace amounts; some vaccines, such as certain multi-dose influenza vaccines, may still contain thimerosal in some jurisdictions. The European Union restricted its use in vaccines for young children, and the World Health Organization states that thimerosal-containing vaccines are safe at approved exposure levels.

In summary, thimerosal is a mercury-containing preservative with a long history of use in vaccines. It is subject to ongoing safety monitoring, with most regulatory authorities finding current exposure levels to be safe for the general population.