Vertical transmission of hepatitis B virus (HBV) from mother to infant during birth is highly efficient. Without prophylaxis, about 30 percent of infants infected with HBV at birth will become chronically infected, placing them at increased risk of liver failure and death. These infected persons also become possible sources of transmission to others. Postexposure prophylaxis consists of administration of 0.5 mL of hepatitis B immunoglobulin (HBIG) and one dose of hepatitis B vaccine (HepB) given intramuscularly at separate sites within 12 hours of birth, followed by two additional doses of HepB given at one to two months and six months of age. This prophylaxis prevents HBV infection in 85 to 95 percent of infants. Postvaccination serologic recheck of hepatitis B surface antigen (HbsAg) and the antibody (anti-HBs) is recommended at nine to 15 months of age to identify infants who may need revaccination or long-term medical management of chronic infection. Euler and associates evaluated this prophylaxis strategy to reduce vertical transmission of HBV at birth.
Using surveillance data collected in Dallas, Tex., the authors evaluated the public health programs involved in the prevention of HBV transmission, the success of the program, and factors associated with eventual development of low or high levels of anti-HBs. Of the 796 live infants born to HBsAg-positive women enrolled in the health department surveillance program, 393 (49 percent) received HBIG and all three hepatitis B vaccinations, as well as serologic testing as scheduled. Fourteen infants tested positive for HbsAg; four of these children did not receive HBIG, six received all scheduled immunoprophylaxis measures on schedule, and the other four were off schedule by five days or less. Of the noninfected infants, 21 (3.4 percent) had anti-HBs levels below 10 when serotested. All but one of these infants received the full prophylaxis course. With revaccination, most children developed anti-HBs with an overall final successful immunization rate of 99 percent. Factors associated with not being serotested postvaccination included being a non-Hispanic white, having a mother younger than 20 years, and being from a low-income household.
The authors conclude that a public-health based surveillance system improves postexposure immunoprophylaxis and postvaccination serotesting rates; however, many children do not complete the vaccination regimen or receive serotesting. With full vaccination, protective levels of anti-HBs are achieved in 91 percent of children, and additional doses after nonprotective serotest results can increase this rate to 98 percent, decreasing the eventual HBs Ag-positive rate to around 2 percent. Postprophylaxis serotesting is best performed within three to four months after receipt of the third dose of vaccine. Infants in the lowest income families (less than $15,000 annual household income) are at the greatest risk for inadequate levels of antibodies.
editor's note: The longevity of the immunity imparted by vaccination during infancy is an important question. Studies of young children nine to 15 years of age who received the full hepatitis B vaccine have shown that more than 50 percent continue to have adequate levels of anti-HBs to represent probable immunity. Some studies have demonstrated ongoing immunity even after detectable anti-HBs declines. Williams and associates further study the persistence of anti-HBs in immunized children, the response to an HbsAg challenge, and the utility of a booster vaccine dose. The authors found that although antibody levels decline within three to four years after the vaccination regimen is completed, there is a high anamnestic response to an HbsAg challenge as well as a very low incidence of HBV infection. They conclude that these findings do not support periodic anti-HBs screening or periodic boosters in children who completed the vaccine series at birth.—r.s.