Vaccine Safety > Issues of Interest > Thimerosal
Implementation Guidance for Immunization Grantees during the Transition Period to Vaccines without Thimerosal
Centers for Disease Control & Prevention (CDC)
July 14, 1999 (contents of this page was accurate only during this time period)

Purpose

This guidance is intended to assist immunization grantee program staff through a temporary transition period during which vaccine manufacturers are working to reduce or eliminate thimerosal from their products in accordance with recommendations contained in the Joint Statement of the Public Health Service (PHS) and the American Academy of Pediatrics (AAP) regarding thimerosal in vaccines (MMWR 1999; 48:563-565). A return to current recommendations is anticipated as soon as adequate supplies of thimerosal-free vaccines are available.

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On July 7, 1999, the American Academy of Pediatrics and the Public Health Service released a joint statement regarding thimerosal in vaccines (Appendix I) which was published in the MMWR. The AAP and the CDC have been developing guidance materials for their constituents. The AAP guidance was issued on July 12, 1999 (Appendix II) entitled "Thimerosal in Vaccines–An Interim Report". This CDC Interim Guidance document takes into consideration both the AAP/PHS Statement and the AAP Interim Report and provides additional information of interest to local and state immunization programs and health care providers participating in the Vaccines For Children program. This guidance also provides an Appendix of Questions and Answers developed by CDC regarding thimerosal that may be helpful in answering questions about programmatic issues (Appendix III).

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The major points in the Joint Statement of the American Academy of Pediatrics and the Public Health Service are:

1. Thimerosal has been used as an additive to biologics and vaccines since the 1930's because it is very effective in killing bacteria used in several vaccines and in preventing bacterial contamination, particularly in opened multi-dose containers. Thimerosal constains a small amount of mercury in the form of ethyl mercury.
   
2. 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.
   
3. There are no guidelines for ethyl mercury, but experts agree that methyl mercury guidelines are appropriate to use in this situation. There is a significant safety margin incorporated into all Federal guidelines on methyl mercury exposure.
   
4. There is no evidence of any harm caused by the level of exposure that some children may have encountered in following the existing immunization schedule.
   
5. The Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agree that the use of thimerosal as a preservative should be removed as soon as possible.
   
6. Clinicians and parents are encouraged to immunize all infants even if the choice of individual vaccine products is limited for any reason.
   
7. The recommendations remain unchanged for routine vaccination with DTaP/DTP, Hib, and for hepatitis B vaccination of infants born to hepatitis B surface antigen (HBsAg) positive mothers or mothers whose HBsAg status is unknown. All products are acceptable including those which contain thimerosal.
   
8. Clinicians and parents can take advantage of the existing flexibility in the immunization schedule to delay hepatitis B vaccination from birth until two to six months for infants born to mothers who are HBsAg negative. More details are offered below.

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Guidelines

For Hib and DTaP/DTP

The PHS and AAP continue to recommend that all children should be immunized against diseases indicated in the recommended immunization schedule. Clinicians and parents are encouraged to immunize all infants even if the choice of individual vaccines is limited for any reason.

The use of products containing thimerosal is preferable to withholding vaccinations which protect against diseases that represent immediate threats to young infants (e.g. DTaP/DTP, Hib, and hepatitis B vaccine for infants at high risk for perinatal and early childhood hepatitis B virus infection.

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For Hepatitis B

The Joint Statement makes suggestions for infant hepatitis B vaccination which take into account 1) the age at the first dose, 2) the hepatitis B surface antigen (HBsAg) status of the mother, and 3) the birth weight and gestational age of the infant.

The Joint Statement reaffirms the recommendations for infants born to HBsAg positive mothers or for infants born to mothers whose HBsAg status is unknown. Therefore, these infants should continue to receive hepatitis B immunoprophylaxis as currently recommended and should receive hepatitis B vaccines as indicated. Currently, no thimerosal-free hepatitis B vaccines are licensed for use at birth. 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.

Many hospitals have instituted policies to vaccinate all children at birth regardless of HBsAg status as a means of ensuring that all the infants of HBsAg positive women and infants of women with an unknown HBsAg status are vaccinated at birth. These hospitals should continue current policies until procedures are or can be put in place to guarantee the proper management of all births to prevent perinatal HBV transmission. Such procedures should ensure that 1) the HBsAg status of every pregnant woman is available and reviewed at delivery, 2) appropriate passive-active immunoprophylaxis (hepatitis B immune globulin [HBIG] and hepatitis B vaccine) is provided for infants of HBsAg positive women within 12 hours of birth, and 3) appropriate active immunoprophylaxis (hepatitis B vaccine) is provided for infants of women with an unknown HBsAg status.

Pregnant women whose HBsAg status is unknown at delivery should have their blood drawn for testing as soon as possible. If test results cannot be obtained within 12 hours of birth, the infant should be vaccinated. Infants of women determined to be HBsAg positive should receive HBIG as soon as possible but within 7 days of birth.

The AAP/PHS Joint Statement and the AAP Interim Report currently do not contain a statement about hepatitis B vaccination for infants born to HBsAg negative women from populations at increased risk of perinatal and early childhood HBV infection.

This CDC Interim Guidance expands on those statements and recommends that hepatitis B vaccination be carried out for infants born to HBsAg negative mothers belonging to populations or groups that have a high risk of early childhood HBV infection, including Asian Pacific Islanders, immigrant populations from countries in which HBV is of high or intermediate endemicity (see Health Information for International Travel, 1999), and households with persons with chronic HBV infection ( HBsAg -positive persons). These infants should receive hepatitis B vaccine at birth.

The Joint Statement emphasizes the existing flexibility in the hepatitis B vaccination schedule for infants born to known or documented HBsAg-negative mothers in order to reduce cumulative exposure to thimerosal. It states: "Clinicians and parents can take advantage of the flexibility within the existing schedule for infants born to hepatitis B surface antigen negative women to postpone the first dose of hepatitis B vaccine from birth until two to six months of age when the infant is considerably larger."

If a decision is made to delay the birth dose of hepatitis B vaccine for infants of HBsAg negative mothers, the CDC prefers that hepatitis B vaccine be administered according to current recommendations of the Advisory Committee on Immunization Practices beginning at two months which is at the lower end of the the 2-6 month age range included in the AAP/PHS Joint Statement.

The Academy of Pediatrics supports the Joint Statement policy but prefers the administration of the first dose of hepatitis B vaccine at two months only if a thimerosal-free vaccine is available. If it is not available, the AAP prefers that the first dose of hepatitis B vaccine be administered at six months.

The Joint Statement contains a precaution about vaccination of premature or low birth weight infants. It states that preterm infants born to HBsAg-negative mothers should receive hepatitis B vaccine, but ideally not until they reach term gestational age and a weight of at least 5.5 lbs (2.5 kg).

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This page last modified on March 28, 2000
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