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Vaccine Ingredients

Vaccines contain ingredients, called antigens, which cause the body to develop immunity. Vaccines also contain very small amounts of other ingredients--all of which play necessary roles either in making the vaccine, or in ensuring that the vaccine is safe and effective. These types of ingredients are listed below.

Type of Ingredient Examples Purpose
Preservatives Thimerosal (only in multi-dose vials of flu vaccine)* To prevent contamination
Adjuvants Aluminum salts To help stimulate the body’s response to the antigens
Stabilizers Sugars, gelatin To keep the vaccine potent during transportation and storage
Residual cell culture materials Egg protein To grow enough of the virus or bacteria to make the vaccine
Residual inactivating ingredients Formaldehyde To kill viruses or inactivate toxins during the manufacturing process
Residual antibiotics Neomycin, sulfa drugs To prevent contamination by bacteria during the vaccine manufacturing process

*Today, the only childhood vaccines used routinely in the United States that contain thimerosal (mercury) are flu vaccines in multi-dose vials. These vials have very tiny amounts of thimerosal as a preservative. This is necessary because each time an individual dose is drawn from a multi-dose vial with a new needle and syringe, there is the potential to contaminate the vial with harmful microbes (toxins).

There is no evidence that the small amounts of thimerosal in flu vaccines causes any harm, except for minor reactions like redness and swelling at the injection site. Although no evidence suggests that there are safety concerns with thimerosal, vaccine manufacturers have stopped using it as a precautionary measure. Flu vaccines that do not contain thimerosal are available (in single dose vials). 

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