Immunoprophylaxis failure of hepatitis B (HBV) remains a concern and has been reported in approximately 10-30% of infants born to highly viremic mothers with HBeAg-positive. Maternal HBV DNA >6log10 copies/mL (or 200,000 IU/mL) is the major independent risk for mother-to-child transmission (MTCT). Two recent random controlled trial (RCT) studies have shown that the use of Tenofovir Disoproxil Fumarate (TDF) in highly viremic HBsAg positive mothers may safely reduce the rate of MTCT when compared between groups of TDF treated and untreated patients. Tenofovir Alafenamide (TAF) is the successor to TDF, and both drugs have a similar mechanism of action to reduce HBV DNA levels and normalize serum alanine aminotransferase (ALT) in chronic hepatitis B patients (CHB) with few adverse effects. TAF however, has a better safety profile with less adverse effects to bone mineral density and renal function. The present prospective, double-arm study is to evaluate the non-inferiority in the efficacy and safety of TAF therapy versus TDF therapy in highly viremic mothers and their infants for the prevention of MTCT in the real world setting.

This is a prospective, double-arm, multi-center study conducted through 11 centers across China. Consecutive 450 mothers who are eligible for the study will be enrolled during gestational weeks 24-28 to receive TDF or TAF based on the patients' preference, and the treatment will be discontinued right after the delivery. All infants will receive HBV vaccination plus HBIg within 12 hours after birth and the additional HBV vaccination at the age of 4 weeks and 24 weeks. Primary outcome assessment will be performed at the infants' age of 28 will be collected to evaluate non-inferiority in the safety and efficacy of TAF therapy versus TDF therapy. These parameters will be extracted from test results of serum biochemistries, hematology, and virology, including but not limited to aspartate aminotransferase (AST), ALT, HBV DNA levels, and serological status of HBV (HBsAg, HBeAb, HBcAb, HBeAg, and HBsAg).

All aforementioned clinical parameters will be extracted from mothers at the following timepoints for assessment: the baseline, i.e. the start of TAF/TDF treatment, gestational weeks 28, 32, 36, on delivery, and at postpartum weeks 24-28. For the infant, information from two timepoints, at birth and at infant age of 28 weeks, will be collected. This information regarding the infant will include the physical parameters weight, height, head circumference, HBV DNA levels, HBV serological status, if they received hepatitis B immunoglobin (HBIg), if they received the complete series of HBV vaccine. All relevant information regarding the patient will be logged into a password-protected computer for primary and secondary analysis.

Group A: 225 participating mothers will receive TAF (oral 25 mg tablet daily) starting at gestational week 24-28 of pregnancy and continue until delivery. The mothers will be followed together with their infants until postpartum week 28.Infants will receive hepatitis B vaccine plus HBIg at birth (within 12 hours) and additional hepatitis B vaccine at the age of week 4 and week 24. Group B: 225 participating mothers will receive TDF (oral 300 mg tablet daily) starting at gestational week 24-28 of pregnancy and continue until delivery. Patients in group B will have similar follow-up schedules as those in the Group A. Infants will receive hepatitis B vaccine plus HBIg at birth (within 12 hours) and additional hepatitis B vaccine at the age of week 4 and week 24.

Inclusion Criteria:

1. Pregnant female, above 18 years of age and under 40 years of age.

2. Gestational age between 12-14 weeks (The screening on patients can be started at gestational week 12).

3. Documented compensated and stable chronic hepatitis B defined by all of the following:

   • HBsAg persistently positive > 6 months.
   • Clinical history, physical findings, and test results are compatible with compensated chronic hepatitis B.

4. Detectable maternal serum HBsAg and HBeAg at the screening visit.

5. Maternal serum HBV DNA levels exceeding 200,000 IU/mL by the COBAS Amplicor HBV PCR assay at screening visits.

6. Patient is willing and able to comply with the study drug regimen and all other study requirements. Patient is also willing to prevent another pregnancy in 28 weeks after delivery of the current baby.

7. Patient and her husband (both father and mother of the child) understand the risk and are willing to have the mother participating in the study. The mother must be willing and able to provide written informed consent to participate in the study.

Exclusion Criteria:

Patients will be excluded if they have any one of the following:

1. Creatinine clearance <100 mL/min (using the Cockcroft-Gault method based on serum creatinine and ideal body weight) or hypo-phosphoremia (below normal range).
2. History of renal events on adefovir or history of resistance to adefovir.
3. Hemoglobin <8 g/dL, or neutrophil count <1000/uL, or ALT >5 times ULN, or total bilirubin >2 mg/dL; or albumin <25gm/L, or abnormal creatinine level, or abnormal BUN levels.
4. History of abortion, or congenital malformation, or child infected with HBV in a prior pregnancy.
5. Biological father of the child (current pregnancy) has CHB.
6. Significant renal, cardiovascular, pulmonary, or neurological disease that may impact the subject's participation in the study as per the opinion of the investigator.

225 consecutive chronically infected hepatitis B mothers who are willing to receive tenofovir alafenamide (TAF) treatment and another consecutive 225 who are willing to receive tenofovir disoproxil fumarate (TDF) treatment at eleven centers across China for high viremic load during pregnancy will be enrolled and followed prospectively for data collection. These patients underwent TAF/TDF treatment in their respective care centers and will be grouped together in Group A for TAF treatment and Group B for TDF treatment for primary and secondary analysis.