United States, but such vaccines are still being produced in other countries. The recombinant hepatitis B vaccines in use in the United States since the late 1980s are produced using Saccharomyces cerevisiae (baker’s yeast), into which a plasmid containing the gene for HBsAg has been inserted (CDC, 1990). The resulting vaccine consists of HBsAg protein adsorbed to aluminum hydroxide. Some recombinant vaccines used in other countries are produced using other methods. Three doses of hepatitis B vaccine are required for full immunization. In the United States, current recommendations call for universal immunization of children, with doses administered at birth, at 1 to 2 months, and at 6 to 18 months. For children born to mothers who are HBsAg-negative, the first two doses can be given at 1 to 2 months and 4 months, respectively.6 Immunization is also recommended for all unimmunized adolescents and for adults at high risk of exposure to HBV. High-risk adults include, but are not limited to, health care workers and public-safety workers who have exposure toblood in the workplace, hemodialysis patients, household contacts and sex partners of HBV carriers, and adoptees from countries where HBV is endemic (CDC, 1991).

SCIENTIFIC ASSESSMENT

Causality

As has been specified, the committee’s review focused on six possible adverse outcomes: multiple sclerosis, acute disseminated encephalomyelitis, optic neuritis, transverse myelitis, Guillain-Barré syndrome, and brachial neuritis.

Most of the epidemiological evidence identified by the committee examines the relationship between exposure to hepatitis B vaccine and the incidence of newly diagnosed cases (incident cases) of MS or of a first episode of a CNS demyelinating disorder (which can be consistent with MS but not yet meet criteria for a diagnosis of MS). One study examined the risk for relapse in patients with diagnosed MS. Some of the studies on MS also examined the risk for other adverse outcomes, but overall, evidence regarding these outcomes is limited. In the one study regarding GBS, the vaccine exposure was to the plasma-derived hepatitis B vaccine, which is no longer produced in the United States. The evidence regarding ADEM, transverse myelitis, and brachial neuritis was primarily case reports.

6  

The percentage of infants receiving the hepatitis B vaccine at birth varies throughout the United States. In 1998, the percentage of infants who received the hepatitis B vaccine at birth was: ≥70% in 13 states; 50–69% in 22 states; and <50% in 15 states (Yusuf et al., 2000). The reason for delaying the birth dose is unknown, though parent and physician preferences, or hospital policy are possibile explanations.



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