48-week end-of-treatment data from theongoing Phase 2 ENSURE study clearly demonstrated the added benefits of elebsiran towards achieving a higher functional cure rate in combination with PEG-IFNα

Data from multiple combination studies sponsored by the Company and itspartner continue to support the Company's strategy of HBV functional cure in broader patient populations with the right combination regimens

DURHAM,N.C. and BEIJING,Nov. 19,2024 --Brii Biosciences Limited ("Brii Bio," or the "Company",stock code: 2137.HK),a biotechnology company developing therapies to improve patient health and choice across diseases with high unmet medical needs,announced new data from its ongoing Phase 2 ENSURE study as a late-breaking oral presentation at the American Association for the Study of Liver Diseases (AASLD) The Liver Meeting®,taking place from November 15 - 19 in San Diego,CA.

ENSURE is an active-controlled and randomized Phase 2 study designed to evaluate the contribution of elebsiran (BRII-835,VIR-2218),an investigational small interfering ribonucleic acid (siRNA),in combination with pegylated interferon alpha (PEG-IFNα)in participants with chronic HBV infection with baseline hepatitis B surface antigen (HBsAg) of 100-3,000 IU/mL. The study excluded HBV patients with low baseline HBsAg levels (<100 IU/mL) to investigate the potential curative benefits in broader patient populations. The ENSURE 48-week end-of-treatment (EOT) data demonstrated that 26.3% (5/19) or 33.3% (6/18) of participants receiving 200 mg or 100 mg elebsiran in combination with PEG-IFNα versus 5.6% (1/18) receiving PEG-IFNα alone achieved HBsAg seroclearance at EOT.

"The EOT data from the ENSURE study are clearcut," said Dr. Jidong Jia,Professor of Medicine at the Liver Research Centre,Beijing Friendship Hospital,Capital Medical University in Beijing,China. "Previous studies have shown that combination of siRNA and PEG-IFNα is one of the most promising therapies to achieve higher HBsAg seroclearance. The ENSURE study marks the first evidence to delineate the contribution of siRNA towards functional cure on top of the well-established PEG-IFNαtherapy. I believe that elebsiran has the potential to make a substantial impact in the pursuit of higher HBV functional cure rates."

"We are encouraged that the data from this trial continue to support our goal of developinga functional cure for chronic HBVin target populations," said David Margolis,MD,Chief Medical Officer of Brii Bio."The results highlight the potential of elebsiran asthe backbone of combination treatment regimens currently being evaluated in several ongoing trials. We look forward to advancing elebsiran through our ongoing Phase 2 studies in combination with other modalities,aiming to deliver higher functional cure rates to 254million patients worldwide living with chronic HBV infection."

Abstract Number: 5008

Late-Breaking Oral Presentation Title: Efficacy and safety of elebsiran (BRII-835) and pegylated interferon alpha (PEG-IFNα) combination therapy vs PEG-IFNα in virologically suppressed participants with chronic hepatitis B virus (HBV) infection: preliminary results

Presenter:Jidong Jia,M.D.,Ph.D.,China

The rates of HBsAg seroclearance at EOT in elebsiran 200 mg + PEG-IFNα and elebsiran 100 mg + PEG-IFNα cohorts were 26.3% (5/19) and 33.3% (6/18),respectively,notably higher compared to PEG-IFNα alone cohort (5.6%).

In the sub-population with baseline HBsAg of 100-1,500 IU/mL,HBsAg seroclearance was achieved in 31.3% (5/16) or 40.0% (6/15) of participants receiving elebsiran 200 mg or 100 mg in combination with PEG-IFNα,respectively.

Greater HBsAg reductions at EOT were observed in elebsiran + PEG-IFNα combination cohorts (mean [SE]: -2.47 [0.28] or -3.01 [0.28] log10 IU/mL in elebsiran 200 mg or 100 mg,respectively) than in PEG-IFNα cohort (-1.02 [0.30] log10 IU/mL).

Elebsiran in combination with PEG-IFNα at both 200 mg and 100 mg doses achieved similar rates of HBsAg seroclearance and reductions in HBsAg levels among participants with baseline HBsAg levels 100-3,000 IU/mL.

Elebsiran and PEG-IFNα combination therapy was generally safe and well tolerated in participants with virally suppressed chronic HBV infection.

Post-treatment follow-up is ongoing and will continue for 24 weeks after discontinuation of treatment.

As part ofBrii Bio's unique approach to developing a functional cure for HBV,the Company and its partners are actively progressing multiple combination studieswith our differentiated portfolio,including elebsiran,tobevibart,an investigational broadly neutralizing monoclonal antibody targeting HBV,and BRII-179,a recombinant protein-based HBV immunotherapeutic. Key data read-outs will be shared in the coming months at the scientific conferences throughout 2025.

About Hepatitis B

Hepatitis B virus (HBV)infection is one of the world's most significant infectious disease threats with more than 254 million people infected globally.[1]Chronic HBV infection is the leading cause of liver disease and an estimated 820,000 people die of complications from chronic HBV infection each year.[1]HBV is of exceptional concern in China,where 87 million people are chronically infected.[2]

About Elebsiran (BRII-835 or VIR-2218)

Elebsiran is an investigational subcutaneouslyadministered HBV-targeting siRNA designed to degrade hepatitis B virus RNA transcripts andlimit the production of hepatitis B surface antigen. It has the potential to have direct antiviralactivity against HBV and HDV. It is the first siRNA in the clinic to include Enhanced StabilizationChemistry Plus technology to enhance stability and minimize off-target activity,which potentiallycan result in an increased therapeutic index. Brii Biolicensed exclusive rights to develop andcommercialize elebsiran for theGreater China territory from Vir in 2020.

About Brii Bio

Brii Biosciences Limited ("Brii Bio",stock code: 2137.HK) is a biotechnology company developing therapies to address major public health challenges where patients experience high unmet medical needs,limited choice and significant social stigmas. With a focus on infectious and central nervous system diseases,the Company is advancing a broad pipeline of unique therapeutic candidates with lead programs against hepatitis B virus (HBV)infection. The Company is led by a visionary and experienced leadership team and has operations in key biotech hubs,including Raleigh-Durham,the San Francisco Bay Area,Beijing and Shanghai. For more information,visit www.briibio.com.

[1] World Health Organization. (April 2024).Global hepatitis report 2024: action for access in low- and middle-income countries.World Health Organization. Retrieved from https://www.who.int/publications/i/item/9789240091672

[2] World Health Organization. Hepatitis. World Health Organization. Retrieved from https://www.who.int/china/health-topics/hepatitis#:~:text=There%20are%2087%20million%20people,living%20with%20chronic%20hepatitis%20C