Vaccines contain components and ingredients that carefully improve the vaccine’s safety and efficacy. The FDA regulations require that vaccines undergo tests to ensure sterility, general safety, purity, identity, suitability of constituent materials and potency. Parents can be assured that components of their child’s vaccines are safe and work to keep children healthy and protected against infectious disease.
In addition to the active ingredient, vaccines contain excipients, or inactive substances that “carry” the active ingredients. Excipients enable the vaccine to do its job, which is to trigger a natural immune response in the body and to produce antibodies that recognize and fight off a particular antigen. Typically, vaccines only have trace amounts of these components – much less than children encounter in their environment, food, and water.
Excipients used in vaccines can be categorized as:
- Adjuvants help promote an earlier, more potent, and more persistent immune response to the antigen.
- Stabilizers increase the storage life of the vaccine.
- Preservatives make multi-dose vials possible.
Common examples of these additive substances used in vaccines include:
- Aluminum gels or salts are added as adjuvants to help the body stimulate a better response to the vaccine. Aluminum also allows for the use of lower dosages.
- Antibiotics prevent the growth of germs (bacteria) during production and storage of the vaccine.
- Egg protein is found in influenza and yellow fever vaccines, which are prepared using chicken eggs. Ordinarily, persons who are able to eat eggs or egg products safely can receive these vaccines.
- Formaldehyde inactivates bacterial products for toxoid vaccines. (These are vaccines that use an inactive bacterial toxin to produce immunity.) It also kills unwanted viruses and bacteria that might contaminate the vaccine during production.
- Monosodium glutamate (MSG) and 2-phenoxy-ethanol are used as stabilizers in a few vaccines to help the vaccine remain unchanged when the vaccine is exposed to heat, light, acidity or humidity.
- Thimerosal is a mercury-containing preservative added to multi-dose vials to prevent contamination and growth of potentially harmful bacteria.
For a list of all vaccine ingredients and which vaccines they’re in, view the CDC Excipient Table.