Some people are concerned about the use of thimerosal, a mercury-containing preservative, in vaccines. The U.S. Food and Drug Administration is the chief federal government agency responsible for regulating vaccines in the U.S. and therefore provides more detailed information on this subject.  To learn more about the use of thimerosal in vaccines, please see these resources:

Food and Drug Administration (FDA)

• Statement on thimerosal in vaccines
• Question and answer: What is thimerosal? Is it safe when used in some vaccines?
• All questions and answers about thimerosal in vaccines

Centers for Disease Control and Prevention (CDC)

• Fact sheet on thimerosal in vaccines 
• Frequent questions about thimerosal 
• List of all vaccines and their ingredients (PDF)(4 pp, 358 K, About PDF)
• Answers to questions about thimerosal in seasonal influenza vaccines
• Main page on vaccine safety