Background and aim: Although immunization of infants against hepatitis B virus (HBV) is the most effective way to prevent infection, duration of the afforded protection is unknown. Titers of anti-HBV antibodies decline with time, especially during the first few years after vaccination. Anti-HBV antibody levels were measured in the serum of vaccinated children in order to determine the duration of the response afforded by the primary course of HBV vaccine.
Methods: The immunity derived from the HBV vaccine was assessed by measuring antibody levels in 122 healthy children who were vaccinated in a routine vaccination program in Israel.
Results: Ninety-four children (77.1%) had detectable antibodies levels (HBsAb titer > or = 10 mIU/ml): 59 (48.4%) of the children had high antibodies levels (HBsAb titer > 100 mIU/ml). Twenty-eight children (22.9%) had undetectable antibodies levels (HBsAb titer < 10 mIU/ml). When the children were divided into three groups according to the time elapsed since vaccination, it was found that the antibody levels declined with time (p < 0.009). Most of the children with undetectable antibody levels belonged to the 5 to 8-y post-vaccination group (36.1% vs 20% and 14.6% for the 2.5 to 5-y and 1 to 2.5-y groups, respectively, p < 0.01). The mean HBsAb declined in relation to the length of time post-vaccination (226.9 +/- 248.2 mIU/ml for 1-2.5 y post-vaccination, 199.0 +/- 235.7 mIU/ml for 2.5-5 y and 90.4 +/- 138.5 for 5-8 y, p < 0.05). No correlation was found between HBsAb titers and gestational age, birthweight and parental origin, although females generated higher mean antibody levels than males (207.3 +/- 217 mIU/ml vs 141.9 +/- 218.9 mIU/ml, p < 0.05).
Conclusion: Our data demonstrate a steady decline in anti-HBV titers over time after routine vaccination against HBV in Israel. The most significant decline occurred 5-8 y post-vaccination.