Hibsago (Bepirovirsen) Japan Approval: CHB Functional Cure and B-Well Data Essentials

　　On 24 August 2026,Japan’s Ministry of Health,Labour and Welfare approved Hibsago(bepirovirsen sodium)for functional cure of adult chronic hepatitis B,representing the first global approval of bepirovirsen.The drug is developed and commercialized by GSK with technology from Ionis and is an antisense oligonucleotide(ASO),usually given subcutaneously.Japanese review used the SENKU innovative-drug pathway;in the United States it has received FDA Fast Track and Breakthrough Therapy designations.

　　Indication and patient selection​

　　The approved Japanese indication covers adults already on nucleos(t)ide analogues for at least 6 months,with baseline HBsAg≤3000 IU/mL and HBV DNA＜90 IU/mL.It is not a universal replacement for all antivirals,but a finite-course option for treated patients who meet predefined virologic criteria and aim for functional cure.

　　Mechanism​

　　Bepirovirsen targets HBV RNA transcripts,reduces production of viral genomic intermediates and hepatitis B surface antigen,and lowers HBsAg burden in blood.By decreasing antigen-mediated immune suppression,it helps the host immune system regain control of HBV.The goal is sustained off-treatment virologic control rather than indefinite suppression alone.

　　B-Well 1/2 phase 3 results​

　　Approval was supported by two global,multicenter,randomized,double-blind,placebo-controlled trials,B-Well 1 and B-Well 2,conducted in 29 countries.In pooled analysis,among participants with baseline HBsAg≤3000 IU/mL,6 months of bepirovirsen produced a 19%functional cure rate(233/1220)versus 0/614 with placebo,p＜0.001.In the lower-antigen subgroup with HBsAg≤1000 IU/mL,the functional cure rate was 26%(200/768).Exploratory analyses showed that many treated participants achieved HBsAg≤100 IU/mL,a level associated with better immune control and long-term outcomes.

　　Functional cure is generally defined as HBsAg loss and HBV DNA below the lower limit of quantification sustained for at least 24 weeks after stopping all therapy,indicating immune control without ongoing medication.

　　Safety and limitations​

　　The safety profile was manageable.The most common reactions were injection-site erythema,local pain,and transient liver enzyme elevations.ALT increases require evaluation together with symptoms,bilirubin,and coagulation,because transaminase flares may reflect immune-mediated responses or hepatic injury.Not all patients achieve functional cure;baseline HBsAg,HBV DNA,prior treatment response,and cirrhosis status affect outcomes.Japan is approved;other regions remain under separate regulatory review,and local labeling should govern use.