FDA approves GSK's Hibsago, first antisense oligonucleotide for chronic hepatitis B

The U.S. Food and Drug Administration announced on October 20, 2026 that it approved Hibsago (bepirovirsen) injection for adults with chronic hepatitis B virus infection who do not have cirrhosis. It is the first antisense oligonucleotide ever approved for the disease and is cleared for use with existing antiviral therapy. The label covers adults who have taken hepatitis B antiviral therapy for at least six months, have suppressed virus levels in the blood and have hepatitis B surface antigen levels of 3,000 IU/mL or less on an FDA authorized test. Hibsago is injected under the skin for up to 24 weeks, and patients continue their existing hepatitis B medicine for at least 24 weeks after the last injection.

Chronic hepatitis B is a serious liver infection that spreads through infected bodily fluids such as blood, saliva and semen. GSK said it affects about 1.7 million people in the United States and more than 240 million worldwide, causes roughly 1.1 million deaths a year and remains the leading cause of liver cancer. Reuters reported on October 20, 2026 that more than 250 million people globally live with the infection. Existing nucleotide analogue treatments are often taken for life. They suppress the virus but rarely eliminate it. GSK said the current standard of care typically achieves less than 1% functional cure after one year, while Reuters put sustained clearance at 1% to 4%.

Functional cure means reducing viral DNA and proteins to undetectable levels, not eradicating every trace of the virus, as Fierce Pharma reported on October 21, 2026. Antisense technology is designed to interfere with the genetic instructions that let the virus reproduce and produce viral proteins. GSK licensed bepirovirsen from Ionis Pharmaceuticals, which is eligible for milestone payments, according to Reuters. The drug is already approved in Japan, where the Ministry of Health, Labour and Welfare cleared it in late August 2026, and it is under review in China and Europe.

The approval rests on the B-Well phase III program. GSK announced on October 20, 2026 that B-Well 1 and B-Well 2 were randomized, double blind, placebo controlled trials in 29 countries. Pooled data showed a 19% functional cure rate, or 233 of 1,220 participants, versus 0 of 614 on placebo at week 72. In a key secondary endpoint, the rate was 26%, or 200 of 768, among participants with baseline surface antigen at or below 1,000 IU/mL, a group representing about 45% of diagnosed chronic hepatitis B cases globally.

Key Facts

The FDA said 24% of Hibsago recipients across two placebo controlled trials met the requirements to stop their existing medicine, versus none on placebo. Twenty four weeks after stopping all hepatitis B treatment, 19% still had the virus under control and no detectable surface antigen. The label carries a boxed warning for serious liver reactions and low platelet counts that can cause life threatening bleeding, plus warnings for worsening kidney function, serious inflammatory reactions such as vasculitis and risks from improper administration. The most common side effects, excluding laboratory abnormalities, were injection site reactions, fever, fatigue and headache. The FDA also authorized the Roche Elecsys HBsAg II quant II RxDx assay as a companion diagnostic to select and monitor patients.

GSK announced on October 20, 2026 that the course is six months, with an option for self administration after the first dose. Exploratory analyses showed bepirovirsen reduced surface antigen to 100 IU/mL or less in 49% of participants, or 598 of 1,220, and in 62% of the lower antigen subgroup, or 476 of 768, as of week 72. GSK described bepirovirsen as a first in class antisense oligonucleotide offering functional cure rates that it called unprecedented compared with current treatment.

Reuters reported on October 20, 2026 that GSK expects peak annual sales of more than £2 billion, or $2.68 billion, for Hibsago, central to its plan to reach more than £40 billion in annual revenue by 2031. Under new chief executive Luke Miels, GSK is trying to speed development and launches ahead of patent expirations on its blockbuster HIV medicines. Reuters also reported that U.S. biotech Aligos Therapeutics is developing a rival therapy, pevifoscorvir sodium, in a mid stage trial. GSK did not immediately respond to a Reuters request for comment on U.S. pricing and commercial availability.

Fierce Pharma reported on October 21, 2026 that the FDA gave the go ahead late Tuesday for use with nucleos(t)ide analogue reverse transcriptase inhibitor therapy in adults without cirrhosis. The publication said the approval brings the antisense oligonucleotide class to hepatitis B for the first time and that the boxed warning could slow adoption. It noted that standard of care nucleoside analogues such as Bristol Myers Squibb's Baraclude and Gilead Sciences' Viread block viral replication but have limited potential to deliver a functional cure. NDTV reported on October 21, 2026 that the FDA approval applies to adults without cirrhosis who have received antiviral therapy for at least six months and have surface antigen levels of 3,000 IU/mL or less.

Analysis

What this really means is that the standard of care for chronic hepatitis B has moved from indefinite suppression alone to a time limited attempt at functional cure for a carefully selected group. The 19% absolute functional cure rate is far below the efficacy seen with many curative regimens in other diseases, but it is a genuine advance against a baseline of zero in the placebo arms and a standard of care that GSK says typically achieves less than 1% functional cure after one year. The 26% rate in patients with baseline surface antigen at or below 1,000 IU/mL is the more clinically relevant number because it identifies the population most likely to benefit. The approval does not mean that most patients will be cured. It means that some patients may be able to stop all hepatitis B treatment without losing viral control.

The label and the warning language will shape adoption as much as the efficacy data. Hibsago is restricted to adults without cirrhosis, with suppressed virus and surface antigen at or below 3,000 IU/mL, and it requires an FDA authorized test to establish eligibility. The boxed warning for serious liver reactions and low platelet counts that can cause life threatening bleeding, plus warnings for worsening kidney function, serious inflammatory reactions such as vasculitis and improper administration, means that patients will need regular blood tests and follow up. Those are manageable for many patients, but they add monitoring burden to a disease that is often managed with generic oral antivirals.

For GSK, the judgement is that Hibsago is strategically important but not an immediate blockbuster without pricing and access clarity. Reuters reported on October 20, 2026 that GSK projects peak annual sales above £2 billion and did not comment on U.S. pricing or near term launch plans. The product is central to GSK's plan to reach more than £40 billion in annual revenue by 2031, and it gives the company a first in class asset as it faces patent expirations on HIV medicines. The Ionis milestone obligations and the Roche companion diagnostic add complexity to the commercial model. Approvals in Japan and reviews in China and Europe give GSK multiple markets, but each will have its own label and reimbursement negotiation.

Why It Matters

The public health stakes are large. GSK said chronic hepatitis B affects about 1.7 million people in the United States and more than 240 million worldwide, causes roughly 1.1 million deaths a year and remains the leading cause of liver cancer. Reuters put the global population at more than 250 million. Current nucleotide analogues are often taken for life and help only 1% to 4% of patients clear the virus for a sustained period, according to Reuters. A six month course that allows some patients to stop all treatment could reduce the cumulative burden of lifelong therapy for a subset of patients.

The approval also matters because it validates antisense oligonucleotides as a treatment modality in infectious disease. The FDA said Hibsago is the first antisense oligonucleotide approved for chronic hepatitis B. GSK licensed the drug from Ionis, and the approval triggers milestone payments. For patients, the practical message is that Hibsago is not a first line option for everyone with hepatitis B. It is for adults without cirrhosis who are already on antiviral therapy, have suppressed virus and have surface antigen at or below 3,000 IU/mL. Wendy Carter, acting director of the Office of Infectious Diseases in the FDA Center for Drug Evaluation and Research, said Hibsago offers some patients the possibility of maintaining control after all treatment has ended and called the approval an important advance.

Next Up

The next step is the U.S. launch. GSK did not comment to Reuters on near term launch plans or U.S. pricing, and those details will determine access. The company is also awaiting regulatory decisions in China and Europe, while Japan has already approved the product. GSK's sales forecast of more than £2 billion at peak will depend on label uptake, diagnostic availability and reimbursement. The approval includes a boxed warning and requires regular blood tests and follow up, so specialty liver clinics will need workflows for patient selection, injection training and monitoring.