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Frequently Asked Questions

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Do vaccines contain toxic ingredients?

Like all medicines, vaccines must undergo several stages of rigorous testing to ensure their safety and effectiveness before they are approved for use by the Biologics and Genetic Therapies Directorate (BGTD) of Health Canada.

What is the key vaccine ingredient?

The main ingredient in most vaccines is an immunogen, the killed or weakened germ (virus or bacterium). It is meant to stimulate the immune system to recognize and prevent future disease. Vaccines differ in term of the type of immunogen that is used. Some newer vaccines are made from only part of the germ's cell (for example, a purified sugar or a purified protein).

What else do vaccines contain?

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Vaccines usually contain sterile water or salt solution. Vaccines may contain the following (PDF Document):

  • Adjuvants help vaccines work better, longer and faster;
  • Added preservatives to keep multi-dose vaccine vials sterile;
  • Antibiotics to prevent bacterial growth during vaccine preparation;
  • Stabilizers to help maintain quality during storage at different temperatures.

What exactly are these other vaccine ingredients?

The most common adjuvants are aluminum salts or alum (aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate). Scientists are discovering new ways alum works, which might help open the doors for creating new vaccines for diseases such as HIV, tuberculosis and malaria.

Aluminum salts are present in vaccines that prevent viral or bacterial diseases such as hepatitis A and B, diphtheria, tetanus, whooping cough. These vaccines are recommended for both children and adults. Alum is not present in live viral vaccines such as those that prevent measles, mumps, rubella, chickenpox and rotavirus.

Aluminum salts have been used safely as vaccine adjuvants since 1926. The amount of aluminum that can be added to vaccines is controlled by Health Canada.

  • Health Canada allows no more than 1.25 mg/single human dose as the safe aluminum level in vaccines. It follows standards such as those established by World Health Organization and the European Pharmacopeia.


A preservative is added to prevent bacterial growth in multi-dose vials.

Thimerosal is the most effective preservative and has been used safely for over seven decades. Most vaccines licensed in Canada do not contain thimerosal. Only influenza vaccine and most hepatitis B vaccines contain thimerosal.

Theoretical concerns regarding possible mercury toxicity and link to autism have been dismissed with multiple studies that have found no evidence of a link.

Thimerosal contains ethyl mercury in an amount well below established limits of safety. Ethyl mercury is eliminated from the body rapidly and does not accumulate, even in premature infants. This is in contrast to methyl mercury which is found in many foodstuffs, especially fish – and which remains in the body longer and can accumulate.

The 2007 National Advisory Committee on Immunization (NACI) statement concluded that "There is no legitimate safety reason to avoid the use of thimerosal–containing products for children or older individuals, including pregnant women."


Stabilizers are substances added to improve the vaccine quality or stability. Substances such as albumin, gelatin, and lactose help to stabilize the immunogens throughout the manufacturing process for example when a product is freeze dried. They also help to prevent loss of immunogen through absorption to the glass vial container.

Other ingredients in small "trace amount"

Other substances used during the preparation of the "immunogen(s)" are removed later in the manufacturing process, to the extent possible, so they remain in very small minute quantity (referred to "a trace"). The only significant concern at this amount would be for possible allergy.

Examples of these include:

  • Some viruses, like influenza, are grown in eggs, and some egg proteins may end up in the final vaccine.
  • Toxins recovered from diphtheria and tetanus must be inactivated with formaldehyde to remove any potential for toxicity.

The ingredients for each vaccine in use in Canada are described in the specific vaccine chapters in the Canadian Immunization Guide, Evergreen Edition.

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