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

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 (\