OBJECTIVETo investigate the dynamic changes of the anti-HBs level among immunized newborn infants born to HBsAg-positive and HBsAg-negative mothers in hyper-endemic area of Hepatitis B.

METHODSInfants who were regularly vaccinated with Hepatitis B vaccine and tested to be anti-HBs positive were divided into two groups according to HBsAg-positive or negative mothers in Long-an, Guangxi. Each subject was followed up 3 times during age 5 to 8. SPRIA was used to test HBsAg, anti-HBs and anti-HBc. Results During the follow-up period, positive rates of anti-HBs in children born to HBsAg-positive mothers ranged between 52.00% and 78.00%, and those with HBsAg-negative mothers was between 43.84% and 54.74%. GMT in two groups was between 55.36 mIU/ml and 95.66 mIU/ml as well as between 39.90 mIU/ml and 65.47 mIU/ml, respectively. There was no statistical significance in both positive rates and GMT between age groups. The anti-HBs level in the follow-up period of children born to HBsAg-positive mothers was higher than that of those born to HBsAg-negative mothers in the same age group. In the age group of 6-8 years with HBsAg-negative mothers, the positive rates in the follow-up period of children with high anti-HBs titers in the primary vaccination were 2.29-2.84 times of those with low titers. The anti-HBs titer of children in a follow-up period was lower than that in the primary vaccination, no matter whether they were born to HBsAg-positive mothers. However, the decline rate of children born to HBsAg-negative mothers was significantly higher than those born to HBsAg-positive mothers (84.91% vs. 61.54%; chi2 = 28.7982, P = 0.000). The incidence rate (25.64%) of a 4-fold increase in antibody titers of children born to HBsAg-positive mothers was significantly higher than that of children born to HBsAg-negative mothers (7.37%) from the primary vaccination to the follow-up period (chi2 = 6.7661, P = 0.009) with was 3.5 times of the latter. Subjects with HBsAg seroconvertion were those with low anti-HBs titers in primary vaccination.

CONCLUSIONThe anti-HBs level decreased slowly in successfully immunized children from age 5 to 8. The chance of natural booster yielded by natural infection increased in immunized children born to HBsAg-positive mothers. The anti-HBs level in the primary vaccination played an important role in prevention of seroconversion of HBsAg.