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Immunization Science

Effects of the Joint Statement on Thimerosal on Hepatitis B Immunization

The article

Hepatitis B vaccine coverage among infants born to women without prenatal screening for hepatitis B virus infection: effects of the Joint Statement on Thimerosal in Vaccines. Thomas AR, Fiore AE, Corwith HL, Cieslak PR, and Margolis HS. The Pediatric Infectious Disease Journal 2004; 23(4): 313-318

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NNii’s explanatory note: In July 1999, the U.S. Public Health Service (US PHS) and the American Academy of Pediatrics (AAP) issued a joint statement that, although there was no known adverse effect from thimerosal in vaccines, it would be prudent to eliminate or reduce the amount of thimerosal (a mercury-containing compound) in vaccines. The joint statement also recommended that, because Hepatitis B vaccine used at that time for infants contained thimerosal, the first dose of hepatitis B vaccine be deferred from birth until 2 to 6 months of age; this was specifically a recommendation only for infants born to women with negative results in hepatitis B pre-natal screenings (HBsAg). Infants born to HBsAg-positive women or to women whose HBsAg status was unknown, were to continue to receive the first hepatitis B vaccine dose within 12 hours of birth.
In September 1999 the CDC announced that a preservative-free hepatitis B vaccine was available and that hepatitis B vaccine should again be provided for all infants at birth. Even after a thimerosal preservative-free vaccine became available, coverage by the time of hospital discharge of women with unknown HBsAg status was still 29% lower than before the recommendation.

The question

What was the effect of the 1999 joint statement on Thimerosal on Hepatitis B vaccine administration to infants born to women whose HBsAg (Hepatitis B infection) status was unknown?

The study

Researchers reviewed electronic birth certificate data from 34 Oregon hospitals during three periods of time. First, from April through June 1999 before the joint statement was issued. Second, from August through October 1999 after the joint statement was released. Third, from April through June 2000 when resumption of pre-1999 practices of routine newborn Hepatitis B immunization should have been fully implemented. They then verified maternal HBsAg screening and newborn hepatitis B vaccination.

The researchers also surveyed the hospitals to determine how many of them stopped routine hepatitis B immunization of newborns and whether they had reinstituted universal newborn Hepatitis B vaccinations once preservative-free vaccines were available as of April 2000.

The findings

The study found the vast majority of women delivering during the study period were of known HBsAg status. However, 298 mothers were found to be of unknown HBsAg status at delivery and 147 of those 298 (49%) mothers were still of unknown status at discharge—which represented 1% of the total births at the 34 hospitals during the time periods studied.

Before the Joint Statement, 27% of infants born to mothers of unknown HBsAg status were vaccinated within 12 hours of birth, and 80% had been vaccinated before hospital discharge. This decreased by 25% (to 2%) and 76% (to 4%), respectively, after publication of the Joint Statement and continued to remain lower than the pre-Joint Statement once thimerosal-free vaccine became available.

Also, before the joint statement, 47 of 54 (87%) surveyed hospitals had policies to provide hepatitis B vaccine to all newborns before discharge. After the joint statement, only 2 (4%) of these hospitals retained their policy to immunize all infants. In May 2001, 8 months after CDC’s recommendation to resume hepatitis B newborn vaccinations, 40 of 54 (74%) hospitals reported that they had reinstated or continued them.

The relevance/bottom line

Misinterpretation of the recommendations in the 1999 joint statement resulted in a significant decline of hepatitis B vaccine coverage for infants born to unscreened women. This coverage remained significantly lower 10 to 12 months later.

NNii’s comments

There is no evidence that thimerosal in vaccines has ever caused a problem. The decision to reduce the exposure of infants to this form of mercury was considered “prudent’ in 1999. The decision to delay the birth dose of hepatitis B vaccine caused great disruption to established immunization programs, and some infants to potentially have been infected with hepatitis B.

Discontinuing an immunization recommendation can be accomplished quickly. Reinstituting the recommendation can be substantially more difficult.

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