Assessment of the anti-hepatitis B vaccination efficacy in high risk children

In October 1995, The Ministry of Health has initiated the national immunization program of newborns against hepatitis B. Owing to the frequency of asymptomatic Hepatitis B clinical forms in children, as well as the deficiencies in the surveillance system, the assessment of the vaccination efficacy can be performed objectively only by the detection of the prevalence of anti HBs antibodies in children to whom the complete three doses of immunization schedule have been administered (at 0, 2 and 6 months of age). We report in this study the results of a seroprevalence research carried out on a group of 272 children from orphanages who have been vaccinated. A protective anti HBs titer (> 10 mIU) was recorded only in 66.3% of cases; other 10 samples contained antibodies at a titer lower than the protective level. In the 80 children without seroconversion the presence of anti HBc antibodies (marker for the natural infection) was investigated. 30% of the seronegative children have anti HBc antibodies from which 54.2% have also HbsAg. Significant differences were recorded in the seroconversion level and in the geometric mean of titers between the various units in which sera were collected. In four orphanages (district Arad, Jassy, Sibiu and Teleorman) the seroconversion exceeded 90%, in 5 orphanages it was over 80% and in the others it ranged from 30% to 70%. The lowest seroconversions were recorded in the orphanages in Bucharest, Botoşani, Galaţi and Olt. The possible causes of the low immunogenicity are analyzed: non-vaccination or incomplete vaccination; low immunoreactivity of children, many of whom are premature; high HbsAg carriage rate among the mother's etc. Although the evolution of the post vaccinal seroconversion is not a routine practice in the appraisement of Hepatitis B vaccine immunogenicity, our results require the extension of the study in order to adopt the most effective vaccinal strategy.