Will the FDA approve bepirovirsen for chronic hepatitis B?

deadline 2026-10-26 confidence high tier 1 evidence

89%PolySignal estimate

Resolution criterion

Resolves YES if the FDA publishes an approval (Drugs@FDA or an official GSK/Ionis press release) for bepirovirsen in chronic hepatitis B on or before 26 October 2026. A complete response letter, a postponement of the PDUFA date, or the absence of a decision count as no.

Verified starting state

Priority Review granted, PDUFA date 26 October 2026. Described by GSK/Ionis as a potential first-in-class antisense oligonucleotide, the first medicine to deliver clinically meaningful functional cure rates in chronic hepatitis B, distinct from existing nucleos(t)ide analogues. (GSK/Ionis press release, 28 April 2026)

What pushes it up

The FDA granted bepirovirsen both Breakthrough Therapy Designation and Priority Review, indicating it addresses a significant unmet need with substantial evidence [4].
The drug has already been approved in Japan (as Hibsago) for the same indication, which serves as a major regulatory validation of the clinical data package [1].
Phase 3 clinical trial results were published in the New England Journal of Medicine and described by GSK as delivering unprecedented functional cure rates [0, 2].
Regulatory reviews are also underway in the EU and China, suggesting a robust global filing strategy [6, 7].

What pushes it down

Manufacturing and product quality issues account for over 50% of Complete Response Letters (CRLs), which can occur regardless of clinical efficacy [15].
Historical data shows that approximately 36% of drugs with new mechanisms fail to achieve approval in their first review cycle.

What would move this number most

The primary uncertainty lies in potential Chemistry, Manufacturing, and Controls (CMC) issues or late-stage safety observations that could trigger a Complete Response Letter despite strong efficacy data.

How this number is built

Deadline	2026-10-26
Base rate	64%
Best evidence	tier 1 · 7 article(s) used
Independent runs	88 · 90 (spread 2 pts)
Confidence	high
Evidence cap	not triggered
Last revised	2026-09-24 09:01
Model	gemini-3-flash-preview

Sources consulted

Bepirovirsen Treatment for Chronic Hepatitis B Virus Infectiontier 1 · NEJM · 2026-09-24 Hibsago (bepirovirsen) approved in Japan as first and only functional cure for chronic hepatitis Btier 1 · GSK (media) · 2026-08-24 Bepirovirsen achieves unprecedented functional cure rates with potential to redefine treatment for chronic hepatitis Btier 1 · GSK (media) · 2026-05-28 Bepirovirsen accepted for priority review and granted Breakthrough Therapy Designation by the US FDAtier 1 · GSK · 2026-04-28 Bepirovirsen accepted for regulatory review in China as a potential first-in-class functional cure for chronic hepatitis Btier 1 · GSK (media) · 2026-03-30 Bepirovirsen accepted for review by the European Medicines Agency as a potential first-in-class treatment for chronic hepatitis Btier 1 · GSK (media) · 2026-03-27 Jefferies (note d'analyste) : répartition des causes de CRL — fabrication >50%, qualité produit 41%, données cliniques 27%. Statistique rapportée par un tiers, pas un fait officiel de niveau 1.tier 3 · Jefferies via presse spécialisée · 2026-09-22

Probability history

2026-09-24 09:01 89% 18 article(s) on file · gemini-3-flash-preview

Reasons not recorded for this revision (detailed history has only been kept since recently).

2026-09-23 09:03 83% 17 article(s) on file · gemini-3.5-flash

Reasons not recorded for this revision (detailed history has only been kept since recently).

2026-09-22 00:41 83% 11 article(s) on file · openai/gpt-oss-20b (Groq)

Reasons not recorded for this revision (detailed history has only been kept since recently).