A 42.9% hepatitis B surface antigen loss rate at end of treatment is a clinically meaningful signal, but the number that will define Brii Bio’s next two years is not found in the ENRICH efficacy readout. It sits inside an arbitration filing with Vir Biotechnology. Without resolution of that dispute over elebsiran’s manufacturing technology transfer, the entire Phase 3 path for the regimen that just produced these results is legally frozen.
The Phase 2b ENRICH study tested BRII-179 as a priming immunotherapy administered before elebsiran and PEG-IFNα in chronic HBV patients. Across two BRII-179 dosing schedules, 98 and 50 patients respectively, HBsAg loss landed at 42.9% and 40.0%, closely tracking the 41.9% seen in ENSURE Cohort 4 among patients with prior BRII-179 exposure. That consistency across multiple study populations is the strongest argument Brii Bio has for calling sequential priming the preferred registrational design. China’s National Medical Products Administration has already engaged on preliminary alignment for a potential registrational study, and BRII-179 holds Breakthrough Therapy Designation from the NMPA, so the regulatory appetite in the Greater China market is real. The ENHANCE concurrent triple-combination arm, by contrast, came in at 25.5% HBsAg loss, below ENSURE Cohorts 2 and 3’s 29.7% benchmark, effectively ruling out that design for advancement.
What the data do not yet answer is durability. HBsAg loss at end of treatment is not functional cure; off-treatment follow-up is required to confirm rebound rates and immunological persistence. The broader field is wrestling with exactly this question: Phase 3 B-Well trials for bepirovirsen, published in the New England Journal of Medicine in May 2026, reported functional cure in roughly 20% of patients, underscoring that durable HBsAg clearance across any mechanism remains difficult to achieve at scale. Brii Bio’s 40-plus percent end-of-treatment figures look impressive against that backdrop, but the post-treatment follow-up data, expected at a scientific conference in the second half of 2026, will determine whether those numbers hold or contract.
The single variable worth tracking is the arbitration timeline. Brii Bio licensed elebsiran’s Greater China rights from Vir Biotechnology in 2020, and that relationship has now become the structural constraint on every clinical and commercial decision downstream. Strong Phase 2b data with no clear path to Phase 3 enrollment is a peculiar position to be in, and how quickly the arbitration resolves will determine whether this efficacy signal ever reaches the 87 million chronically infected patients in China it was designed to serve.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
