Table 1.

Key components of approved vaccines in the U.S. reproduced from the CDC [46].

Type of Ingredient	Example(s)	Purpose
Preservatives	Thimerosal (only in multi-dose vials of flu vaccine)	To prevent contamination
Adjuvants	Aluminum salts *	To help boost the body’s response to the vaccine
Stabilizers	Sugars, gelatin	To keep the vaccine effective after manufacture
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	To prevent contamination by bacteria during the vaccine manufacturing process

* Aluminum salts have been the only adjuvant used in most FDA-approved and licensed vaccines in the U.S.A.; other adjuvants such as ASO4, ASO1, etc. have also received FDA approval during the past decade, but not for vaccines used in children currently.