For people with chronic hepatitis B, treatment has usually meant a daily pill, taken indefinitely, that keeps the virus quiet without removing it. On October 20, the US Food and Drug Administration approved a drug built to do something different: a six-month course of injections intended to let the immune system keep the virus in check once treatment stops. GSK, the drug's maker, announced the approval of Hibsago (bepirovirsen) in a regulatory filing, after Japan became the first country to approve it in August 2026.

A first, with a narrow target

Bepirovirsen is a first-in-class antisense oligonucleotide, a short strand of genetic material designed to block production of hepatitis B proteins, GSK says. The approval is for chronic hepatitis B in adults, with an option for self-administration after the first dose. The FDA acted ahead of its October 26 decision date, according to GSK's earlier disclosures. Applications are under review in the European Union and China, per GSK's filings.

The target is large. About 75 million people in China live with chronic hepatitis B and roughly 3.2 million in Europe, according to GSK, and the infection is a leading cause of liver cancer. Those figures come from the company's regulatory announcements, not independent estimates.

What "functional cure" means

The term is easy to misread. Functional cure, as defined by GSK and the trial protocol, means that both hepatitis B virus DNA and the viral surface protein HBsAg are undetectable in the blood for at least 24 weeks after all treatment has stopped. The virus is not eradicated from the body. The immune system is controlling it without medication.

That matters because current standard therapy, nucleos(t)ide analogue pills, suppresses the virus but rarely clears the protein. GSK puts the functional cure rate with standard treatment at typically around 1 percent, and says many people remain on treatment indefinitely and still face the risk of serious liver complications.

What the trials showed

The approval rests on two phase 3 trials, B-Well 1 and B-Well 2, which enrolled more than 1,800 non-cirrhotic adults in 29 countries, according to the published trial summaries. All participants were already virologically suppressed on nucleos(t)ide therapy and had HBsAg levels between 100 and 3,000 IU/mL. They were randomized two to one to receive 300 mg of bepirovirsen weekly for 24 weeks, or a placebo, on top of their existing treatment.

Functional cure at week 72 was reached by 20 percent of bepirovirsen patients in B-Well 1 and 19 percent in B-Well 2, compared with none on placebo, according to results published in the New England Journal of Medicine on May 28. Pooled, that was 233 of 1,220 patients versus 0 of 614. Among patients with HBsAg of 1,000 IU/mL or lower, the pooled rate was 26 percent.

Those are strong numbers against a placebo rate of zero. They are also the numbers for people selected to be the most likely to respond.

Who it is for, and who it is not

The label and the data describe a specific group: adults with chronic hepatitis B who are suppressed on current treatment, without cirrhosis, and with relatively low HBsAg levels. People with very high surface antigen levels or advanced liver disease were not in the pivotal trials. One trade publication estimated that the lower-antigen subgroup, at 1,000 IU/mL or below, approximates 45 percent of diagnosed people globally. That is a single outlet's estimate, but it points to the central fact: most patients will not achieve functional cure with this drug.

An independent summary of the NEJM data put it plainly: the majority of patients do not achieve functional cure with bepirovirsen alone. A one-in-five result is a breakthrough for a disease where the rate was near zero. It is not yet a cure for everyone.

The safety trade-off

The side effects are not trivial. In the pooled analysis, serious adverse events occurred in 7 percent of bepirovirsen patients versus 4 percent on placebo, while grade 3 or higher events were more frequent, at 16 percent versus 3 percent, according to the NEJM report as summarized by aidsmap. Injection-site reactions were the most common effect, and a rise in the liver enzyme ALT was the most common severe event, in about 6 percent of treated patients. Only 3 percent stopped treatment because of side effects.

Liver enzyme flares deserve context. In a hepatitis B drug, an ALT flare can mean the immune system is attacking infected liver cells, which is part of how a functional cure may be achieved, but it also means that patients need monitoring. Professor Seng-Gee Lim, who presented the data, suggested that substantial ALT elevation indicated that bepirovirsen was working, according to aidsmap. That interpretation is a clinician's view rather than a proven mechanism, and it is a reason the drug is likely to be used under specialist supervision.

What remains unknown

Several questions are open. The first is durability: how many of the patients who reached functional cure stay in it for years, a question GSK is following in a long-term study of earlier participants. The second is access: the company has not disclosed prices in the material reviewed, and the European and Chinese decisions are still pending. The third is combination use. GSK has started a trial of a sequential regimen with another hepatitis B RNA drug, daplusiran/tomligisiran, to try to reach a broader group of patients.

The wider significance is the shift in goals. China's national hepatitis action plan for 2025 to 2030 already lists functional cure as a treatment target, GSK noted. The measure of this approval will be how many people it reaches, and how many of them hold the response after the first year.

For patients, the practical step is to ask about antigen levels. The result that decides eligibility is not the viral load most people track, but the quantity of surface antigen in the blood, and few patients know their number.

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