QUESTION:
Why do vaccines contain "additives"? Are they harmful?

ANSWER:
Tiny amounts of three types of substances are added to vaccines to ensure that the vaccine is sterile, effective and safe. The following ingredients may be used in the preparation of some vaccines:

• Adjuvants increase the vaccine's ability to stimulate the body's immune system to fight off disease. Adjuvants also help promote a quicker, more potent and persistent immune response to disease. Some examples of adjuvants include aluminum gels or salts.
• Stabilizers help maintain the vaccines' effectiveness even when they are exposed to dramatic changes in the environment (such as temperature, light, humidity, etc). Stabilizers include monosodium glutamate (MSG) and
  2-phenoxyethanol.
• Preservatives are used to prevent bacteria or fungus from contaminating the vaccine, which could cause serious infections in anyone receiving the vaccine. Antibiotics, (i.e. neomycin and streptomycin), formaldehyde and thimerosal may be used for this purpose.

If you want specific information on the additives used in a particular vaccine, ask your doctor or nurse for a copy of the vaccine's package insert. Each vaccine comes with an insert listing every ingredient. The insert also lists every known reaction ever reported, regardless of how minor.

QUESTION:
What is thimerosal?

ANSWER:
Thimerosal is a mercury-based preservative used since the 1930's that prevents vaccines from becoming contaminated with bacteria or fungi. When more than one dose of vaccine is contained in a vial (known as a "multidose" vial), there is a higher risk that the vaccine could become contaminated. Multi-dose vials typically have rubber-like stoppers. Health care workers must puncture the stopper with a needle to withdraw a dose of the vaccine; hence, the stopper encounters multiple punctures as subsequent doses are withdrawn. This can allow bacteria to enter the vial and contaminate the vaccine. If vaccine from a contaminated vial is then injected into a child, this could lead to a serious infection. Preservatives are not needed for vaccines in single-dose vials.

Thimerosal is made of thiosalicylic acid and a form of mercury called "ethylmercury." Ethylmercury is processed by the body and eliminated quickly through the urine. More information is known about methylmercury, because this form of mercury accumulates in the body and remains bound to body tissues for longer periods of time. Federal safety standards for mercury are based on studies performed on methylmercury.

QUESTION:
Can my child have vaccines that don't contain thimerosal?

ANSWER:
Yes! All routinely recommended childhood vaccines are now thimerosal-free. Other vaccines (e.g. influenza; tetanus and diphtheria vaccine for children seven years of age and older and adults) continue to use thimerosal as a preservative in trace amounts.

QUESTION:
What prompted the recommendation that thimerosal be removed from childhood vaccines?

ANSWER:
There has been a public health effort to reduce exposure to mercury from all sources. Exposure to mercury is cumulative and toxic levels of mercury exposure have a wide range of adverse health effects.

In July 1999, the U.S. Public Health Service, the American Academy of Pediatrics and the vaccine manufacturers agreed that thimerosal should be removed from childhood vaccines as a precautionary measure. Their concern was based on the possibility that some infants who received several vaccines in the first six months of life might exceed the acceptable limits of mercury set by one federal agency.

There has been no evidence that receiving multiple thimerosal-containing vaccines in the first six months of life has harmed an infant. However, because of the theoretical possibility that problems with the nervous system could occur, vaccine manufacturers were asked to stop using thimerosal as a preservative.

Single-dose vials have largely replaced multidose vaccine vials and do not require the use of preservatives. Other preservatives that don't contain mercury can be used in some vaccines.

QUESTION:
Has the thimerosal in vaccines been shown to be harmful to children?

Note: Thimerosal has been removed from all routinely recommended childhood vaccines, except some influenza (flu) vaccine, and tetanus-diphtheria (Td) vaccine used in individuals seven years and older.

ANSWER:

A summary of the evidence demonstrating that the thimerosal in vaccines has not been shown to be harmful to children is online at www.immunize.org/safety/thimerosal.htm

Studies have not shown any evidence that the mercury contained in vaccines cause harm. In October 2001, the U.S. Institute of Medicine (IOM) concluded that the evidence does not support that thimerosal exposure through the recommended childhood immunization schedule has caused neurodevelopmental disorders. Some swelling and redness at the injection site may, however, occur for those who are allergic or sensitive to thimerosal.

Other studies that have shown no link between thimerosal and neurodevelopmental disabilities, including autism, are:

• 2004: The IOM Immunization Safety Review Committee concluded that: 1) there is no association between autism and vaccines that contain thimerosal as a preservative, and 2) there is no evidence for the hypothesis regarding a link between autism and vaccines that contain thimerosal.
  
  
• 2003: Part of the system to monitor for vaccine safety is the Vaccine Safety Datalink (VSD) project, which includes medical data on a large number of people at large health maintenance organizations (HMO). As of November 2003, CDC has not found any evidence from the VSD project that neurodevelopmental disabilities such as autism are caused by vaccines containing thimerosal. This finding is consistent with scientific evidence to date.

For more information on thimerosal, visit CDC's National Immunization Program at www.cdc.gov/nip or call their Hotline at 1-800-232-2522(English), 1-800-232-0233 (Spanish) or 1-800-243-7889 (TTY).