Vaccine Safety

Frequently Asked Questions

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Do vaccines contain toxic ingredients?

Answer: The main ingredient in most vaccines is the killed or weakened germ (virus or bacterium), which stimulates our immune system to recognize and prevent future disease. Some newer vaccines are made from only part of the germ's cell (for example, a purified sugar or a purified protein).

• In addition, vaccines usually contain sterile water or salt solution.
• Some vaccines are prepared with a preservative or antibiotic to prevent bacterial growth.
• Some vaccines also contain substances known as stabilizers, to help maintain quality during storage.
• Some vaccines contain an "adjuvant". These substances work to boost our immune response to the vaccine and make it more effective. The amount of any of these ingredients in a vaccine is extremely small, and every batch of vaccine is tested for safety and quality in Canada before it is released for public use.

A preservative called thimerosal received attention in the U.S. in 1999 because it contains mercury and it is used in some vaccines for children. As a precaution, U.S. authorities recommended that the use of vaccines containing thimerosal be reduced or eliminated. In 2001, an independent panel of the U.S. Institute of Medicine conducted an extensive review of this concern. The panel found no evidence that the amount of mercury in childhood vaccines causes damage to a child's nervous system. In Canada, the only routine vaccine for children that contained thimerosal was the hepatitis B vaccine. Canadian infants were never subject to the same level of mercury exposure from vaccines as U.S. infants. A new formula for hepatitis B vaccine, with no thimerosal, is now available. Meanwhile, research into whether thimerosal in vaccines is truly a risk to infants is continuing.

The ingredients for each vaccine in use in Canada is described in the specific vaccine chapters in the Canadian Immunization Guide, 7th Edition 2006.

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