Thiomersal (thimerosal) is added as a preservative. Eli Lilly has developed the vaccine preservative thiomersal (also called merthiolate and thimerosal). Most vaccines do not contain thimerosal. Thiomersal (INN), or thimerosal (USAN, JAN), is an organomercury compound. Certain vaccines contain a compound called thimerosal, which is an organic compound that contains mercury. Mercola has asserted that thimerosal, a vaccine preservative, is harmful due to its mercury content. Single dose vials do not contain thimerosal. In Canada, different variants contain five and 50 micrograms of thimerosal per dose. Thimerosal is used in these multi-dose vials to prevent contamination from multiple preparations. Congress repealed the thimerosal provision following expressions of public displeasure.