Bepirovirsen Achieves 19% Functional Cure Rate in Pivotal Hepatitis B Trials, Redefining Treatment

The B-Well Trial Results at a Glance

The B-Well 1 and B-Well 2 studies enrolled over 1,800 participants across 29 countries and tested bepirovirsen alongside standard-of-care oral antivirals . Both trials independently met their primary endpoint, and the pooled analysis confirmed statistically significant and clinically meaningful results .

Functional Cure Rates

In the overall study population — adults with baseline HBsAg levels at or below 3,000 IU/ml — bepirovirsen plus standard of care delivered a 19% functional cure rate (233 of 1,220 patients). Patients who received standard of care plus placebo saw a 0% functional cure rate (0 of 614 patients), a difference that was highly statistically significant (p<0.001) .

A pre-specified subgroup of patients with lower baseline viral activity (lower HBsAg levels) experienced an even stronger effect: a 26% functional cure rate compared to 0% with standard of care alone . The precise threshold for this subgroup has not yet been detailed in full publications, but the trend toward greater benefit in patients with less entrenched infection is clear.

Durability of Response

Functional cure in these trials required maintaining undetectable virus and lost surface antigen for 24 weeks after completing the six-month bepirovirsen course . This off-treatment durability is what separates a genuine functional cure from a transient response, and the data suggest the immune control achieved is lasting — at least over the measurement period. Longer-term follow-up will be needed to confirm whether this control persists for years.

Safety and Tolerability

Bepirovirsen’s safety profile in the Phase 3 program was consistent with earlier studies and was considered acceptable for a chronic treatment course . Treatment-emergent adverse events were mostly mild to moderate in severity .

The most common side effects, occurring more frequently with bepirovirsen than with placebo, were:

• Injection-site reactions
• Pyrexia
• Fatigue
• Increased alanine aminotransferase (ALT) levels

Importantly, no new or unexpected safety signals emerged in the Phase 3 program beyond what had already been observed in Phase 2b trials . The ALT flares observed were generally transient and self-resolving, a known phenomenon in drugs that trigger immune-mediated clearance of infected liver cells .

Regulatory Pathway and Approvals Timeline

Bepirovirsen is now under active regulatory review in two major markets, backed by Breakthrough Therapy designations that underscore the unmet need and the strength of the clinical data.

United States (FDA)

• Accepted for Priority Review: April 28, 2026
• Breakthrough Therapy Designation granted
• PDUFA goal date: October 26, 2026

The Priority Review timeline of six months (compared to the standard 10 months) reflects the FDA’s view that bepirovirsen could represent a significant improvement over available therapies .

China (NMPA)

• New Drug Application accepted for review: March 30, 2026
• Breakthrough Therapy Designation in China granted: August 2021

China carries the world’s largest burden of chronic hepatitis B infection, making the NMPA’s swift acceptance of the application a critical step for global access . GSK has indicated that further global regulatory filings are planned beginning in Q1 2026, with the US and China as the initial priority markets .

A First-in-Class Mechanism of Action

Bepirovirsen is an antisense oligonucleotide and represents a fundamentally different approach from existing hepatitis B antivirals. It has a triple-action mechanism that targets multiple steps in the HBV lifecycle :

• Reduces viral DNA by recruiting the enzyme RNase H to degrade HBV messenger RNA.
• Suppresses hepatitis B surface antigen (HBsAg) by blocking translation of viral proteins.
• Inhibits pregenomic RNA, the template the virus uses to replicate.

Existing nucleos(t)ide analogues only suppress viral DNA polymerase. Bepirovirsen, by also reducing HBsAg levels, may help restore the patient’s own immune response to the virus — a critical step for achieving sustained, off-treatment control .

What This Means for Patients and Clinical Practice

The implications of the B-Well data extend beyond the numbers. For the first time, a finite-duration treatment has produced functional cure rates that clearly surpass the status quo. Current clinical guidelines acknowledge that lifelong oral antiviral therapy is burdensome, requires regular monitoring, and rarely results in cure . Bepirovirsen offers the possibility of a six-month treatment window after which some patients can stop all medication entirely .

For health systems managing the estimated 254 million people living with chronic hepatitis B globally — including approximately 1.7 million in the United States — the shift could be profound, reducing long-term treatment costs and the risk of liver cirrhosis and hepatocellular carcinoma in cured patients .

That said, a 19% overall cure rate means that the majority of patients did not achieve functional cure. The 26% response in the lower-viral-activity subgroup underscores the importance of patient selection. As full trial data are published and presented — GSK has stated they will appear at the European Association for the Study of the Liver (EASL) Congress — identifying baseline factors that predict response will become a central clinical question .

Caveats and Unanswered Questions

While the Phase 3 results are practice-changing in their potential, several important caveats apply:

• Data maturity: As of mid-2026, the detailed efficacy and safety results from B-Well 1 and B-Well 2 have been disclosed through press releases and regulatory filings from GSK and Ionis. A peer-reviewed publication has not yet appeared .
• Response durability: Functional cure was measured 24 weeks after treatment cessation. Whether patients remain HBsAg-negative and HBV DNA undetectable for years beyond this window — and whether this translates into reduced rates of liver cancer — remains unknown.
• Non-responders: The biology of why 74–81% of patients did not achieve functional cure on bepirovirsen is not yet characterized. This could include differences in viral integration, host immune fitness, or the timing of intervention.
• Combination potential: GSK and Ionis have indicated that bepirovirsen could serve as a backbone for sequential treatment strategies, implying that future regimens may combine it with other novel agents to increase cure rates further .