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Centers for Disease Control and Prevention

Vaccines & Immunizations

Basics and Common Questions:

Ingredients of Vaccines - Fact Sheet

Chemicals are used in food and medicines to prevent the growth of harmful germs and reduce spoilage; in vaccines, chemical compounds are used to inactivate (kill) a virus or bacteria or stabilize it, helping to preserve the vaccine and keep it effective and sterile. Chemical components used as preservatives in vaccines occur in very small quantities, far too small to provoke a serious allergic response in most people.

Chemicals commonly used in the production of vaccines include a suspending fluid (sterile water, saline, or fluids containing protein); preservatives and stabilizers (for example, albumin, phenols, and glycine); and adjuvants or enhancers that help improve the vaccine's effectiveness.

What You Should Know

  • Millions of doses of vaccines are administered to children in this country each year. Ensuring that those vaccines are potent, sterile, and safe requires the addition of minute amounts of chemical additives.
  • Chemicals are added to vaccines to inactivate a virus or bacteria and stabilize the vaccine, helping to preserve the vaccine and prevent it from losing its potency over time. One such chemical is called an excipient is an inactive substance used as a carrier for the active ingredients found in medication.
  • The amount of chemical additives found in vaccines is very small and may not be enough to cause a serious allergic response.
  • In July 1999, the Federal government asked vaccine manufacturers to work towards eliminating or reducing the use of thimerosal, a preservative which contains small amounts of mercury, in any products currently available on the market. Today, all routinely recommended pediatric vaccines manufactured for the U.S. market contain no thimerosal or only trace amounts.

Reference Materials

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Additional Facts

Additives used in the production of vaccines may include

  1. suspending fluid (e.g. sterile water, saline, or fluids containing protein);
  2. preservatives and stabilizers to help the vaccine remain unchanged (e.g. albumin, phenols, and glycine); and
  3. adjuvants or enhancers that help the vaccine improve its work.

Common substances found in vaccines include:

  • Aluminum gels or salts of aluminum which are added as adjuvants to help the vaccine stimulate production of antibodies to fight off diseases and aid other substances in their action. In vaccines, adjuvants may be added to help promote an earlier response, more potent response, or more persistent immune response to disease.
  • Antibiotics which are added to vaccines to prevent the growth of germs (bacteria) in vaccine cultures.
  • Egg protein which is found in vaccines prepared using chick embryos. Ordinarily, persons who are able to eat eggs or egg products safely can receive these vaccines.
  • Formaldehyde which is used to inactivate bacterial products for toxoid vaccines, (these are vaccines that use a weakened or suppressed bacterial toxin to increase a response to an antigen or a disease, such as the tetanus toxoid used to prepare tenanus vaccinations; toxoids are too weak or suppressed to be harmful). It is also used to kill unwanted viruses and bacteria that might be found in cultures used to produce vaccines.
  • Monosodium glutamate (MSG) and 2-phenoxy-ethanol which are used as stabilizers in a few vaccines to help the vaccine remain unchanged even in the presence of forces such as heat, light, acidity, humidity etc. MSG is also found in many foods, especially Asian foods and flavor enhancers.
  • Thimerosal which is a preservative that might be added to prevent the vaccine from spoiling. Thimerosal is also found in some contact lens solutions and throat sprays.

For children with a prior history of allergic reactions to any of these substances in vaccines, parents should consult their child’s health care provider before vaccination.

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What You Can Do

  • To find out what chemical additives are in specific vaccines, ask your health care provider or pharmacist for a copy of the vaccine package insert, which lists all ingredients in the vaccine and discusses any known adverse reactions.
  • To ensure the safety of vaccines, the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), the National Institutes of Health (NIH), and other Federal agencies routinely monitor and conduct research to examine any new evidence that would suggest possible problems with the safety of vaccines. To keep abreast of the latest information, continue to reference these materials.
  • To report a health problem that followed vaccination you or your provider should call the Vaccine Adverse Event Reporting System (VAERS) at 1-800-822-7967.

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For More Information

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This page last modified on April 4, 2008
Content last reviewed on April 30, 2007
Content Source: National Center for Immunization and Respiratory Diseases

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Vaccines and Immunizations