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 muta-tion 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 differ-ent 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 immunoprophy-laxis 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 .%目的：探讨在当前联合免疫方案下，发生乙肝母婴传播免疫预防失败过程中乙型肝炎病毒（ HBV） S基因的突变特征。方法：选择15例分娩免疫失败婴儿的孕妇及其联合免疫前的新生儿和免疫后的7月龄婴儿，将母亲、新生儿和婴儿分别配对，对其外周血中HBV的S基因（包括前 S和S）分2个片段进行PCR扩增测序，对比母亲、新生儿及婴儿3组间HBV基因型、前S和S基因突变率及突变位点的不同。结果：（1）新生儿和婴儿体内HBV的基因型与母亲完全相同。（2）3组2个片段的突变率差异均无统计学意义（P＞0．05）；同源树簇集分析中，母亲与所分娩的新生儿和婴儿体内HBV均形成各自独立的簇集。（3）突变位点：母亲-新生儿（13对）：7例新生儿与母亲体内的HBV存在不同的突变位点（共15个位点）；新生儿-婴儿（13对）：3例婴儿与新生儿体内的HBV存在不同的突变位点，即nt273A→A/G、nt512C→C/T和nt1139C→A（共3个位点），前2个位于S区的“a”决定簇之外，后1个则在与X编码框重叠的区域；婴儿-母亲（15对）：有9例婴儿与母亲体内的HBV存在不同的突变位点（共25个位点），但仅1例是母亲、新生儿和免疫后婴儿均存在不同的突变位点。结论：（1）新生儿及免疫后婴儿体内的HBV均源自于母亲；（2）HBV的S基因在联合免疫前和免疫后均可发生突变，主要发生在联合免疫前，是否与免疫失败有关尚需进一步研究。
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