Paired study on hepatitis B virus S gene mutation in immunoprophylaxis failure to prevent HBV vertical transmission

AIM：To explore the characteristics of hepatitis B virus S gene mutation in the vertical transmission after active and passive vaccination. METHODS：Fifteen cases of immunoprophylaxis failure were enrolled in the study. HBV S gene (including pres-S and S) from the mothers, newborns before active and passive vaccination and 7-month-old infants with immunoprophylaxis failure were detected by PCR amplification. The characteristics of HBV S gene mutation were compared among the 3 groups. RESULTS：The genotype of HBV in the newborns and the infants was the same as that in the mothers. The frequencies of mutation in the 2 fragments of the HBV S gene had no significant difference between the 3 groups. The homology tree model based on HBV S gene was analyzed in the 3 groups, in which every group had their own cluster. There were 15 different mutation sites between 7 pairs of mothers and newborns. There were 3 different mutation sites between 3 pairs of newborns and infants (nt273A→A/G, nt512C→C/T and nt1139C→A), among which the first 2 were located in the S gene region but not in the “a” determinant, and the latter was located in the overlap region of S and X genes. There were 25 different mutation sites between 9 pairs of mothers and infants, but only 1 case had a different mutation site between the mother, newborn and infant. CONCLUSION：The HBV species in newborns and infants with immunoprophylaxis failure were transmitted from the mothers. The mutations in the HBV S gene with immunoprophylaxis failure happened before and after active and passive vaccination, mainly before vaccination. The relationship between HBV S gene mutations and immunoprophylaxis failure should be further explored.