Brii Biosciences Announces the Completion of Enrollment in the Phase 3 National Institutes of Health (NIH) ACTIV-2 Trial, Evaluating the BRII-196 and BRII-198 Monoclonal Neutralizing Antibody Combination for the Treatment of COVID-19

846 outpatients at high risk of clinical progression have been enrolled in the ACTIV-2 phase 2/3 clinical study,from sites in the United States,Brazil,South Africa,Mexico and Argentina.

The participants are being evaluated for the combined endpoint of hospitalizations and death relative to placebo,in the 28 days following treatment.

DURHAM,N.C. and BEIJING,Aug. 5,2021 --Brii Biosciences Limited ("Brii Bio" or the "Company",stock code: 2137.HK) a multi-national company developing innovative therapies for diseases with significant unmet medical need and large public health burden,today announced that the Phase 3 portion of the ACTIV-2 study evaluating its monoclonal neutralizing antibody combination therapy,BRII-196/BRII-198 ("CombinationBRII-196/BRII-198"),has completed enrollment of 846 participants,in sites in the United States,Mexico and Argentina.

The Phase 3 portion of the ACTIV-2 trial,which is sponsored by the National Institute of Allergy and Infectious Diseases (NIAID),part of the NIH,evaluates outpatients at high risk of clinical progression who presented with symptomatic COVID-19 both early (≤5 days) and late (5-10 days) following symptom onset. The participants enrolled are being evaluated for the combined primary endpoint of hospitalizations and death,relative to placebo,in the 28 days following treatment. Upon completion of the study,the analysis of the ACTIV-2 dataset will include participants enrolled between January and July of 2021 – a period of rapid global emergence of novel SARS-CoV-2 variants. Data on the clinical efficacy of combination BRII-196/BRII-198 by variant type will also be evaluated as part of the study analysis. The ACTIV-2 study design provides a unique opportunity to evaluate how the length of time prior to initiating therapy as well as SARS-CoV-2 variants,may impact clinical outcomes following treatment with the combination BRII-196/BRII-198. Current in vitro pseudovirus testing data suggests that combination BRII-196/BRII-198 retains activity against major SARS-CoV-2 variants of concern,including the following commonly identified variants,B.1.1.7 (Alpha),(B.1.351 (Beta),P.1 (Gamma),B.1.429 (Epsilon) and B.1.617.2 (Delta).

Combination BRII-196/BRII-198 was generally safe and well tolerated in Phase 1 and Phase 2 clinical trials conducted to date. ThePhase 2 clinical trial in China(NCT04787211) is ongoingled by Dr. Nanshan Zhong,the Academician of the Chinese Academy of Engineering and Director of the National Clinical Medical Research Center for Respiratory Diseases at the First Affiliated Hospital of Guangzhou Medical University. In response to the recent emergence of COVID-19 cases in China,including cases caused by the Delta variant,Brii Bio has cooperated with governmental agencies and hospitals in China to supply BRII-196/BRII-198 for emergency use in Guangzhou,Shenzhen,Ruili,Kunming,Nanjing and Yangzhou.

About ACTIV-2

The ACTIV-2 trial (NCT04518410) is sponsored by NIAID,one of the institutes of the NIH,and is led by the NIAID-funded AIDS Clinical Trials Group (ACTG). ACTIV-2 is part of NIH's Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV),a public-private partnership program to create a coordinated research strategy that prioritizes and speeds development of the most promising treatments and vaccines.

The ACTIV-2 master protocol evaluates the safety and efficacy of investigational agents for the treatment of symptomatic non-hospitalized adults with COVID-19 under a randomized,blinded,controlled adaptive platform. Participants identified as being at high risk for progression to more severe disease,were eligible for enrollment onto combination BRII 196/BRII-198 or placebo. Phase 3 of the study was designed to determine if combination BRII-196/BRII-198 prevents the composite endpoint of either hospitalization or death through study day 28. The Phase 3 stage was a continuation of the Phase 2 stage in which combination BRII-196/BRII-198 met pre-defined,study-defined safety and efficacy criteria.

About BRII-196 and BRII-198

BRII-196 and BRII-198 are non-competing SARS-CoV-2 monoclonal neutralizing antibodies derived from convalesced COVID-19 patients. They have been specifically engineered to reduce the risk of antibody-dependent enhancement and prolong the plasma half-lives for potentially more durable treatment effect. Their non-overlapping epitope binding regions provide a high degree of neutralization activity against SARS-CoV-2. Current in vitro evidence suggests that combination BRII-196/BRII-198 retains activity against major SARS-CoV-2 variants of concern,B.1.429 (Epsilon) and B.1.617.2 (Delta).

Investigational New Drug applications have been submitted for the combination therapy to the U.S. Food and Drug Administration (FDA),the China National Medical Products Administration (NMPA) and the Department of Health in Hong Kong,China. Combination BRII-196/BRII-198 were generally safe and well tolerated in Phase 1 studies,supporting evaluation in later stage studies. In addition to the collaboration with NIAID,Brii Biosciences is conducting additional studies in China,evaluating the pharmacokinetics and safety of combination BRII-196/BRII-198 as well as a Phase 2 efficacy study of combination BRII-196/BRII-198 for the treatment of COVID-19.

About Brii Biosciences

Brii Biosciences Limited ("Brii Biosciences",or the "Company",stock code: 2137.HK) is a biotechnology company based in China and the United States committed to advancing therapies for significant infectious diseases,such as hepatitis B virus (HBV),human immunodeficiency virus (HIV),multi-drug resistant (MDR) or extensive drug resistant (XDR) gram-negative infections and other illnesses,such as the central nervous system (CNS) diseases,which have significant public health burdens in China and worldwide. For more information,visit www.briibio.com.

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