Study of Tenofovir Alafenamide (TAF) in Children and Teen Participants With Chronic Hepatitis B Virus Infection

Key Inclusion criteria:

• Males and non-pregnant, non-lactating females

• Weight at screening as follows:

• Cohort 1 = ≥ 35 kg (≥ 77 lbs)

• Cohort 2 Group 1 = ≥ 25 kg (≥ 55 lbs)

• Cohort 2 Group 2 = ≥ 14 kg to < 25 kg (≥ 30 lbs to <55 lbs)

• Cohort 2 Group 3 = ≥ 10 kg to < 14 kg (≥ 22 lbs to < 30 lbs) or

• 14 kg to < 25 kg (≥ 30 lbs to < 55 lbs)

• Willing and able to provide written informed consent/assent (child and parent/legalguardian)

• Documented evidence of CHB (eg, HBsAg-positive for ≥ 6 months)

• HBeAg-positive, or HBeAg-negative, chronic HBV infection with all of the following:

• Screening HBV DNA ≥ 2 × 10^4 IU/mL

• Screening serum ALT > 45 U/L (> 1.5 × ULN: 30 U/L) and ≤ 10 × ULN (by centrallaboratory range)

• Treatment-naive or treatment-experienced will be eligible for enrollment.

• Estimated creatinine clearance (CLCr) ≥ 80 mL/min/1.73m^2 (using the Schwartzformula)

• Normal ECG

Key Exclusion criteria:

• Females who are pregnant or breastfeeding

• Males and females of reproductive potential who are unwilling to use an "effective",protocol-specified method(s) of contraception during the study.

• Coinfection with hepatitis C virus (HCV), HIV, or hepatitis D virus (HDV)

• Evidence of hepatocellular carcinoma (Note: if screening alpha-fetoprotein (AFP) is < 50 ng/mL no imaging study is needed; however, if the screening AFP is > 50 ng/mLan imaging study is required)

• Any history of, or current evidence of, clinical hepatic decompensation

• Abnormal hematological and biochemical parameters

• Chronic liver disease of non-HBV etiology (e.g., hemochromatosis, alpha-1antitrypsin deficiency, cholangitis)

• Received solid organ or bone marrow transplant

• Currently receiving therapy with immunomodulators (eg, corticosteroids), orimmunosuppressants

• Significant renal, cardiovascular, pulmonary, or neurological disease in the opinionof the Investigator

• Malignancy within the 5 years prior to screening. Individuals under evaluation forpossible malignancy are not eligible.

• Current alcohol or substance abuse judged by the investigator to potentiallyinterfere with subject compliance.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.