According to the US Centers for Disease Control and Prevention, '''Thimerosal''' is "a [[Mercury (element)|mercury]]-containing preservative that has been used in some [[vaccines]] and other products since the 1930's."<ref> Centers for Disease Control and Prevention, Vaccines & Immunizations Glossary, entry for Thimerosal [http://www.cdc.gov/vaccines/about/terms/glossary.htm#t] ''Thimerosal is a mercury-containing preservative that has been used in some vaccines and other products since the 1930's. There is no evidence that the low concentrations of thimerosal in vaccines have caused any harm other than minor reactions like redness or swelling at the injection site. However, in July 1999 the U.S. Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated from vaccines as a precautionary measure. Today, all routinely recommended childhood vaccines manufactured for the U.S. market contain either no thimerosal or only trace amounts.''</ref> "Thimerosal consists of 49.6% ethyl mercury, an anti-bacterial, anti-fungal that allows manufacturers to sell the vaccine in large, multi-dose containers without fear of contamination."<ref>Journal Sentinel, ''Most flu shots contain mercury, but few know it, Experts say vaccine's benefits outweigh potential risk'', by Raquel Rutledge, Nov. 13, 2007 [http://www.jsonline.com/story/index.aspx?id=685311]</ref> [[Mercury (element)|Mercury]] has long been known to be highly toxic.
According to the CDC, "In July 1999 the U.S. Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated from vaccines as a precautionary measure." <ref> Centers for Disease Control and Prevention, Vaccines & Immunizations Glossary, entry for Thimerosal [http://www.cdc.gov/vaccines/about/terms/glossary.htm#t]</ref> It has since been removed from all early childhood vaccines. Today, the government claims that all routinely recommended childhood vaccines manufactured for the [[United States]] [[market]] contain either no thimerosal or only trace amounts.<ref> Centers for Disease Control and Prevention, Vaccines & Immunizations Glossary, entry for Thimerosal [http://www.cdc.gov/vaccines/about/terms/glossary.htm#t]</ref> But physicians continued to use vaccines containing thimerosal long after the recommendation of its elimination, in order to clear the old inventory of pharmaceutical companies.
About 80% of flu vaccines contain thimerosal -- 25 micrograms of [[mercury]] -- as of 2007. As reported in the Milwaukee Journal-Sentinel:<ref>http://www.jsonline.com/story/index.aspx?id=685311</ref>