Decline of hepatitis B antibody level in vaccinated 5-7 year-old children

Background:�Vaccination is the best way to prevent hepatitis B infection. The efficacy of hepatitis B vaccine and duration of protection after vaccination in infants is unknown. The aim of this study was to evaluate the immunity level of school age children against HBV in order to determine the decline of   hepatitis B antibody level during the childhood period.

Materials and Methods:�This cross-sectional research was performed on 729, 5-7 year-old children  in Kohgiloyeh& BoyerahmadProvince who had been vaccinated at birth.  Patients selected by multiple stage sampling method. While interviewing parents the questionnaire were completed. The laboratory rep[ort was attached to the questionnaire. After confirming the correct date of vaccination time, parents were asked for an informed consent. From each patient  3ml blood sample were taken and hepatitis B surface antibody (HBs-Ab) and hepatitis B surface antigen (HBs-Ag) were determined by ELISA method.  Chi-squared and t-tests were used to analyze obtained data by using SPSS-15 software.

Results:�HBs-Ag was negative in all patients. 84.4% of subjects were immune against HBV (had protective antibody titer). The mean antibody titer was 308.9±230.5 IU/ml with range of 10.6–1175 IU/ml. 15.6% of samples had non protective antibody titer and mean antibody titer was 4.97 ±3. 5 IU/ml. Anti-HBsAb titers were related to the age and residency of children. The immunity level decreased with increasing age. No statistically significant differences could be found between two sexes.

Conclusion: Based on this stud, the immunity persistency rate in this age group was suitable compared to other studies. Unfortunately, there is about 20% of non-immune children to HBV infection in this susceptible age with a high risk of contamination and affliction. Because of seriousness of HBV infection proper immunization strategy should be considered in this era by health care authorities