Babies 411 -Ingredients of Vaccines or Immunizations | Immunizations

The major ingredient of any vaccine is a killed or weakened form of the disease organism the vaccine is designed to prevent. In addition, vaccines can contain:

Diluents: Liquids used to dilute a vaccine to the proper concentration. Usually saline or sterile water is used.
Adjuvants: Chemicals added to vaccines to make them provide stronger immunity. Various forms of aluminum salts are the most commonly used adjuvants in vaccines.
Preservatives: Included in some vaccines (mainly ones that come in multiple-dose vials) to prevent bacterial growth that could contaminate the vaccine. Thimerosal (mercury) is an example of a preservative that is no longer used in REQUIRED vaccinations. Optional vaccinations may still contain thimerosal. Mercury is a known neurotoxin which can damage the neurological system. Most thimerosal containing vaccines are made with 0.01% mercury. Ask your pediatrician for thimerosal-free vaccines if you are concerned.

Stabilizers: Keeps vaccines safe and effective under different conditions and/or temperatures. Examples include gelatin, albumin, MSG, glycine and lactose-sorbitol.
Remnants from manufacturing: Chemicals that are used during the vaccine manufacturing process and then removed from the final product. For example, formalin might be used to kill a vaccine virus, or antibiotics might be used to prevent bacterial contamination. When these chemicals are removed, a tiny trace may remain. The “package insert” that comes with each vial of vaccine lists all the contents of the vaccine and explains why each substance is there. Examples include formaldehyde, antibiotics, or egg and yeast protein.

Read the CDC's Parent's Guide to Childhood Immunizations to learn more.