Vaccines contain small amounts of specific ingredients (also called components), all of which play necessary and important roles during vaccine production. All of these ingredients are safe in the amounts used in vaccines.
What's in vaccines?
Vaccines contain small amounts of either the whole disease germ (virus or bacteria) or parts of the disease germ. These components (also called “antigens”) can be considered the active ingredients in vaccines because they are what cause our immune system to develop protection.
The germs in vaccines are either weakened or killed. Vaccines that contain weakened live versions of the whole germ (such as the Measles, Mumps, Rubella (MMR) and Chickenpox (varicella) vaccines) will not cause the disease in a person with a good immune system. However, live vaccines are not given to people with very weak immune systems as they may develop the disease the vaccine is meant to protect against. Your health care provider will review your (or your child's) medical history before administering a live vaccine to make sure it is safe to receive.
Vaccines that contain killed germs cannot cause the disease, even in people with very weak immune systems. This is because a germ has to be alive to cause disease.
What are some of the other ingredients in vaccines?
Vaccines contain small amounts of specific ingredients (also called components), all of which play necessary and important roles.
Some of these ingredients (such as aluminum salts) help the vaccine to be more effective and others (such as gelatin and albumin) help to keep the vaccine stable during transport and storage. Vaccines contained in multi-dose vials need to contain a preservative to prevent germs from growing in the vial after the first dose has been removed. The preservative thimerosal is no longer used in routine childhood vaccines in Canada, with the exception of influenza vaccines produced in multi-dose vials.
Vaccines may also contain very small (‘trace’) quantities of materials that were used in earlier stages of their production process, like antibiotics (used to prevent the growth of germs) and egg protein (used to grow the virus used to make the vaccine).
Are the ingredients in vaccines safe?
The ingredients in vaccines have been carefully studied for a long time, and are safe in the small amounts used in vaccines. You may have heard or read that some ingredients are harmful, but this is true only at much higher amounts. Any substance, even water, can be harmful at a high dose. There is no evidence that any of the ingredients in these small amounts can cause harm.
These ingredients have not been linked to disease or illness, with the exception of allergic reactions in people with hypersensitivity to a specific ingredient. Before administering a vaccine, your health care provider will ask you about any known allergies or previous reactions to vaccines and will assess whether any given vaccine is not safe for you to receive. If you have an unexpected allergic reaction after receiving a vaccine, your health care provider will be able to recognize and treat it quickly.
Learn more about the ingredients in vaccines by exploring the infographic below.
Where can I find a list of the ingredients in each vaccine?