[Identification of risk factors related to the failure of immunization to interrupt hepatitis B virus perinatal transmission].

OBJECTIVE: To explore the factors influencing failure of an immunization to interrupt perinatal (mother-to-child) transmission of hepatitis B virus (HBV).

METHODS: Between June 2006 and March 2010, a total of 1355 pregnant women testing positive for the hepatitis B surface antigen (HBsAg), at gestational weeks 20 to 42, and without use of antiviral or immunomodulatory drugs during the pregnancy were prospectively recruited to the study. The mothers were given a choice of receiving hepatitis B immunoglobulin (HBIG; three 200 IU intramuscular injections give at four-week intervals starting from gestation week 28) or not. All neonates (1360, including five sets of twins) received hepatitis B vaccine (10 mug) plus HBIG (200 IU) combined immunization within 24 h of birth, as early as possible. Peripheral venous blood samples were collected from the neonates within 24 h of birth and at 7 and 12 months of age for detection of HBV markers, including hepatitis B e antigen (HBeAg) and HBV DNA. The infants were classified according to HBV perinatal transmission status (infection group and non-infection group) and various factors (maternal-related: age, gravidity, parity; pregnancy/birth-related: threatened premature labor, complications; neonate-related: sex, birth weight, apgar score) were compared between the two groups by using non-conditional logistic regression analysis to determine their potential influence on failure of immunization to inhibit transmission.

RESULTS: After 12 months of follow-up, 1.54% (21/1360) of the neonates had presented with HBV infection. Analysis of the HBV-infected neonates revealed differences in infection rates between neonates born to mothers with HBIG injection (2.22% vs. without HBIG injection: 1.11%, P less than 0.05) and caesarean section (1.35% vs. vaginal delivery: 1.73%) but neither reached statistical significance (P less than 0.05); only the practice of breastfeeding showed a significant difference for infection rate, with neonates fed artificial formula having higher infection rate (3.13%) than the breastfed neonates (0.27%, P less than 0.05). The neonate HBV infection rate was also significantly higher for neonates born to HBeAg-positive mothers (4.44% vs. HBeAg-negative mothers: 0%, P less than 0.05) and HBV DNA-positive mothers (3.13% vs. HBV DNA-negative mothers: 0%, P less than 0.05). When the mothers were stratified by serum level of HBV DNA, there was a significant difference in HBV-infected neonates born to mothers with more than or equal to 1*10(7) IU/ml(6.01% vs. 10(3)-10(6) IU/ml: 0.56% and less than 1*10(3) IU/ml: 0%, both P less than 0.05). Logistic regression analysis indicated that the independent risk factors for HBV perinatal transmission despite immunization were maternal serum HBeAg-positive status (relative risk (RR)=31.74, 95% confidence interval (CI): 3.88-259.38) and maternal HBV DNA of ≥ 10⁷ copies/mL (RR=22.58, 95% CI: 4.75-107.40).

CONCLUSION: Failure of vaccine plus HBIG to interrupt mother-to-child transmission of HBV is influenced by maternal serum HBeAg-positive status and maternal HBV DNA of ≥10⁷ copies/mL.