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U.S. Public Health Service
American Academy of Pediatrics
July 10, 1999

Mercury & Thimerosol Vaccine Preservative

This fact sheet contains information about the vaccine preservative thimerosol and childhood immunizations.

WHAT IS THIMEROSAL?

Thimerosol is a mercury-containing preservative used in vaccines since the 1930's to prevent bacterial contamination. Some but not all of the vaccines routinely used for child immunizations contain thimerosol. Based on recent information, on July 7, 1999 the U.S. Public Health Service and the American Academy of Pediatrics stated that mercury levels may exceed a federal limit of acceptability in some children who receive multiple thimerosol containing vaccines in the first six months of life.

 

WHAT DO THE ACCEPTABLE LEVELS OF MERCURY MEAN?

Several federal agencies have set limits for the amount of mercury a person can safely be exposed to. These levels have a wide safety margin such that levels close to the limit are unlikely cause health problems. In the case of mercury exposure from thiomersal in vaccines, levels may be over the acceptable limit set by one federal agency but are below the limit set by two other agencies. Mercury is very common in our environment and there are similar levels for the amount of mercury people can safely consume from eating certain types of fish.

ARE THERE ANY HEALTH EFFECTS FROM THOMEROSAL IN VACCINES?

There are no reports of health problems related to vaccines containing thiomersal. However, we know from persons who have been exposed to high levels of mercury that abnormalities of the nervous system can result. Lower levels of mercury can result in problems with coordination, vision and learning. Because of this, public health officials have decided to eliminate any exposure to thiomersal in vaccines.

WHY ARE PUBLIC HEALTH OFFICIALS CONCERNED ABOU THIMEROSAL?

The concern is because of the possibility that some infants who receive multiple vaccines containing thiomersal might exceed one of the acceptable limits for mercury. There is no evidence that the levels of mercury that an infant receiving multiple thiomersal-containing vaccines in the first six months of life might be exposed to would result in any symptoms, however there is a theoretical possibility of problems of the nervous system. Because of this, vaccine manufacturers have been asked to stop using thiomersal as a preservative.

WHAT DO I NEED TO KNOW ABOUT MY CHILD'S IMMUNIZATIONS?

All the currently recommended childhood vaccines should still be given. The risk of any problem from thiomersal is only theoretical while the risk of serious illness including death from vaccine-preventable diseases is real. All children should continue with the recommended vaccines. The only exception to this is for infants born to mothers who are not hepatitis B carriers. These infants may have their hepatitis B immunizations delayed from birth until 2-6 months of age. Please discuss any questions regarding your child's immunization schedule with your pediatrician or health care provider.

MY CHILD IS OVER SIX MONTHS OLD – DO I NEED TO DO ANYTHING SPECIAL ABOUT THIS PROBLEM?

No – the concern about mercury levels pertains to infants less than six months of age. Mercury exposure from thiomersal is not a problem for children over 6 months of age.

WHERE CAN I GET MORE INFORMATION ON THIMEROSAL AND VACCINES?

Contact your child's health care provider for more information on thimerosal and specific vaccines that your child received and with any questions about your child's health. Additional information is also available on the CDC's website or by calling the CDC's National Immunization Information Hotline at 1-800-232-2522.

All information is general in nature and is not intended to be used as a substitute for appropriate professional advice, contact your physician or healthcare provider for more information.

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