Vaccine Additives

Vaccines often contain antibiotics as well as preservatives to prevent bacteria from growing, stabilizers to maintain the vaccine’s effectiveness, and adjuvants to stimulate production of antibodies. Although present only in minute amounts, these additives play an important role in vaccines. Some vaccine additives, such as thimerosal, aluminum, and formaldehyde, are controversial.


Antibiotics prevent germs from growing in the vaccine cultures.  Neomycin is commonly used, but penicillin and related antibiotics are not used in vaccines because many people are allergic to them.


Vaccine vials that contain several doses need preservatives because each time a needle enters the vial there is a risk of contamination.  Thimerosal is an extremely good preservative, but it is controversial because almost half of its contents is mercury, which is known to cause developmental problems in children when taken in large enough quantities. Formaldehyde, or formalin, is used to inactivate the polio vaccine virus in IPV and to kill germs in the cultures used to produce other vaccines.


Stabilizers maintain vaccine effectiveness despite heat, light, or other adverse conditions. Sulfites and monosodium glutamate (MSG), also found in many foods and alcoholic beverages, are used to stabilize some vaccines.


Aluminum, in the form of aluminum gels or salts of aluminum, is added to vaccines to help prompt antibodies to respond. For example, tetanus and diphtheria toxoids and pertussis vaccine are bound to aluminum salts.

This information is excerpted from the book Vaccinating Your Child: Questions and Answers for the Concerned Parent (Peachtree Publishers, Ltd., 2000). The book’s authors are Dr. Sharon G. Humiston, a pediatrician and clinical researcher at the CDC and the University of Rochester, and Cynthia Good, an award-winning journalist and host of the television show “Good for Parents”.