This is a global multi-center, long-term follow-up study to assess durability of efficacy, as measured by maintenance of treatment response from the parent study, in participants who participated in a previous bepirovirsen study and achieved a complete or partial response. Eligible participants will be enrolled in this study after completing the end of study (EoS) visit in the respective parent bepirovirsen studies (studies B-Clear [209668: NCT04449029], B-Together [209348: NCT04676724], B-Fine [212602: NCT04544956], B-Well 1 [202009: NCT05630807], B-Well 2 [219288: NCT05630820], and TH HBV ASO-001 [217023: NCT05276297]). Participants will be categorized as Not-on-NA, NA-cessated, or On-NA based on their nucleos(t)ide analogue (NA) status in the parent study. No further treatment with bepirovirsen will be administered in this study.

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

  1. 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
  2. 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

  1. NA cessated at Week 48 in parent study and achieved at least HBsAg <1 IU/ml and HBV DNA \

IPD for this study will be made available via the Clinical Study Data Request site.

IPD will be made available within 6 months of publishing the results of the primary endpoints, a key secondary endpoints and safety data of the study.

Access is provided after a research proposal is submitted and has received approval from the Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension can be granted, when justified, for up to another 12 months.