A. Thimerosal is a very effective preservative that contains mercury and has been used in some vaccines and other products since the 1930s.
Thimerosal is the most widely used preservative in vaccines.
The FDA estimates that it is used in more than 30 licensed vaccines and biologics. Mercury is excreted from the body over time. A. Thimerosal is used as an extra safeguard against contamination. It may be used during processing or added to the final container to prevent contamination when multi-dose vials are opened. Before Thimerosal was marketed in the United States, a number of safety studies were conducted, first on animals and then on humans.