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

Infant Vaccines Containing Thimerosal May Exceed Federal Thresholds for Mercury Levels

DETROIT - ( The American Academy of Pediatrics (AAP) and the U.S. Public Health Service (PHS) have released a joint statement on the potential for exceeding a federal acceptable threshold for cumulative levels of mercury in infants receiving Thimerosal–containing vaccines in the first six months of life.  Thimerosal is a mercury-containing preservative present in many but not all vaccine preparations.

Excessive levels of mercury may cause adverse neurodevelopmental effects; however, there is no evidence that such adverse effects actually occur among children exposed to thimerosol in vaccines. Because of the theoretical risk of adverse effects from mercury accumulation, changes are being instituted in vaccine manufacturing processes to eliminate any exposure to mercury.

In order to minimize exposure to thimerosal at this time, changes based on the flexibility in the hepatitis B vaccination schedule should be considered for infants born to hepatitis B surface antigen (HbsAg)–negative mothers. Such infants should have the first dose of hepatitis B vaccine postponed from birth until 2 to 6 months of age. Pre-term infants born to hepatitis B surface antigen–negative mothers should likewise have the first dose of hepatitis B vaccine delayed until they reach term gestational age and a weight of at least 2.5 kg. Because of the substantial risk of disease, there is no change in the recommendations for infants of HbsAg-positive mothers or of mothers whose status is not known.  Also, in populations where HbsAg screening of pregnant women is not routinely performed, vaccination of all infants at birth should be maintained, as is currently recommended.  No other changes in currently recommended practices are indicated.

Both the PHS and AAP continue to recommend all children be immunized according to the current child immunization schedule.

The recognition that some children could be exposed to a cumulative level of mercury over the first six months of life that exceeds one of the federal guidelines on methyl mercury now requires a weighing of two different types of risks when vaccinating infants. On the one hand, there is the known serious risk of diseases and deaths caused by failure to immunize our infants against vaccine-preventable infectious diseases; on the other, there is the unknown and probably much smaller risk, if any, of neurodevelopmental effects posed by exposure to thimerosal. The large risks of not vaccinating children far outweigh the unknown and probably much smaller risk, if any, of cumulative exposure to thimerosal-containing vaccines over the first six months of life.

Nevertheless, because any potential risk is of concern, the Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agree that thimerosal-containing vaccines should be removed as soon as possible.

For your information we have attached a Table listing the thimerosol status of available vaccine products as well as a page of "Frequently Asked Questions" on this subject.

The US Public Health Service and the American Academy of Pediatrics are working collaboratively to assure that the replacement of thimerosal-containing vaccines takes place as expeditiously as possible while at the same time ensuring that our high vaccination coverage levels and their associated low disease levels throughout our entire childhood population are maintained.

The key actions being taken are:

1. A formal request to manufacturers for a clear commitment and a plan to eliminate or reduce as expeditiously as possible the mercury content of their vaccines.

2. A review of pertinent data in a public workshop.

3. Expedited FDA review of manufacturers' supplements to their product license applications to eliminate or reduce the mercury content of a vaccine.

4. Provide information to clinicians and public health professionals to enable them to communicate effectively with parents and consumer groups.

5. Monitoring immunization practices, future immunization coverage, and vaccine-preventable disease levels.

6. Studies to better understand the risks and benefits of this safety assessment.

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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