Routine vaccination of children is one of the most important medical advances of the twentieth century. Important concerns about vaccination include the child's age and underlying medical conditions, disease burden, vaccine efficacy, adverse reactions, and official recommendations.
In the United States the estimated number of persons chronically infected with hepatitis B virus (HBV) is 1.25 million, 36% of whom acquired HBV during childhood. HBV infection becomes chronic in 90% of those infected as infants, 30%-60% of those infected before the age of 4 years, and only 5%-10% of those infected as adults. Each year, HBV infects about 78,000 persons de novo and kills about 6000. Up to 25% of individuals infected with HBV as infants will die of HBV-related chronic liver disease as adults.
HBV transmission occurs primarily by blood exchange or by sexual contact with persons who are either acutely or chronically infected. In 30%-40% of cases, the source of infection is not identified. Some cases may result from inapparent contamination of skin lesions or mucosal surfaces: hepatitis B surface antigen (HBsAg) has been found in impetigo, in saliva, and on toothbrush holders of persons chronically infected with HBV. HBV can be transmitted between young children.
Rationale for Routine Hepatitis B Vaccination
Although anti-HBV antibody levels diminish following vaccination, most persons remain protected through the immunologic memory in recruited lymphocytes. Immunologic memory and the long incubation period of HBV infection allow most immunized persons with low titers to mount a protective anamnestic immune response.
The number of vaccine doses administered, intervals between doses, genetics, prematurity, and underlying medical conditions affect immunogenicity. After the third dose of hepatitis B (HepB) vaccine, more than 95% of children seroconvert. Titers improve with longer intervals between the second and third doses so the vaccine series does not need to be restarted regardless of dose delay. Efficacy for HepB vaccine is high. Prematurity with low birth weight and immunosuppression are associated with lower rates of seroconversion. HepB vaccination should be delayed in preterm infants weighing less than 2 kg until 1 month of age or hospital discharge, whichever first, unless the mother is HBsAg-positive or has unknown HBsAg status, in which case the vaccine should be given within 12 hours of birth.
After administration of HepB vaccine, 3%-9% of children have pain at the injection site; 8%-18% have mild, transient systemic adverse events such as fatigue and headache; and 1%-6% have temperature higher than 37.7°C (99.8°F).
The comprehensive US hepatitis B vaccination policy includes: (1) prevention of perinatal HBV infection, (2) routine vaccination of infants (Figure 7-1), (3) catch-up immunization of adolescents not previously vaccinated, and (4) catch-up immunization of young children at high risk for infection (http://www.cdc.gov/vaccines/vpd-vac/hepB/default.htm#recs).