Long-term Follow-up Study to Evaluate Durability of Treatment Response in Previous Bepirovirsen Study Participants (B-Sure)

Inclusion criteria

• Participants who enter the study on stable NA are willing and able to cease their NA treatment in accordance with the NA cessation schedule.
• Capable of giving informed consent.

For participants rolling over from 209668 (B-Clear), 209348 (B-Together), and 212602 (B-Fine):

• Participants who have previously received at least one dose of bepirovirsen AND

• Achieved the PSPO in the parent study and who maintained a response until the End of Study (EoS) visit in their parent study (defined as complete responders to bepirovirsen from the parent study) OR
• Demonstrated hepatitis B virus surface antigen (HBsAg) reduction greater than or equal to (≥) 1.0 log10 international units per milliliter (IU/mL) from parent study Baseline with HBsAg levels less than (<) 100 IU/mL and HBV deoxyribonucleic acid (DNA) < lower limit of quantification (LLOQ) for 24 weeks after the actual end of treatment regimen, in the absence of rescue medication and maintained until their EoS visit in the parent study.

For participants rolling over from 202009 (B-Well1) and 219288 (B-Well 2):

• Participants who have previously received at least 1 dose of bepirovirsen (or matching placebo where appropriate) AND

• NA cessated at Week 48 in parent study and achieved at least HBsAg <1 IU/ml and HBV DNA <LLOQ at the EOS visit (Week 96) in the parent study OR
• Achieved NA cessation criteria at Week 48 in parent study but have not stopped NA treatment, and are maintaining at least HBsAg <1 IU/ml and HBV DNA <LLOQ at EOS visit (Week 72) of parent study OR
• Did not achieve NA cessation criteria in parent study but achieved at least HBsAg <1 IU/ml and HBV DNA <LLOQ at EOS visit (Week 72) of parent study.

For participants rolling over from 217023 (TH HBV ASO-001):

• Participants who have previously received at least 1 dose of bepirovirsen AND

• Achieved HBsAg <1 IU/ml and HBV DNA <LLOQ in parent study at Week 66 (ASO12 arm) or Week 78 (ASO 24 arm) and are maintaining HBsAg < 1 IU/ml and HBV DNA <LLOQ, at the EOS study visit [Week 133 ASO12 arm), or Week 145 (ASO24 arm)] in parent study OR
• Did not achieve HBsAg <1 IU/ml and HBV DNA <LLOQ in parent study at Week 66 (ASO12 arm) or Week 78 (ASO24 arm) but have achieved HBsAg < 1 IU/ml and HBV DNA < LLOQ by the EOS visit (Week 133 (ASO12 arm) or Week 145 (ASO24 arm)) in the parent study.

Exclusion criteria

• Participants who have/or are currently participating in another non-GSK interventional clinical study exploring HBV treatment since completing their treatment with bepirovirsen.
• Any condition which, in the opinion of the investigator or Medical Monitor, contraindicates their participation in this study.