Atea Pharmaceuticals Reports Fourth Quarter and Full Year 2025 Financial Results and Provides Business Update Advanced Global Phase 3 Program for Treatment of Hepatitis C Virus (HCV) in 2025 with Topline Results from Nor

Atea Pharmaceuticals Reports Fourth Quarter and Full Year 2025 Financial Results and

Provides Business Update

Advanced Global Phase 3 Program for Treatment of Hepatitis C Virus (HCV) in 2025 with Topline Results from North American C-BEYOND Trial Expected Mid-2026 and Topline Results from C-FORWARD Trial Outside North America Anticipated Year-End 2026

Presented Results Reinforcing Bemnifosbuvir/Ruzasvir as a Potential Best-in-Class Regimen for the Treatment of HCV at the 2025 EASL Congress and The Liver Meeting

2025, the Annual Meeting of AASLD

Physician KOLs Underscored the Need for a New Optimized HCV Regimen to Address Treatment Paradigm

Shifts, Including Test-and-Treat Model of Care

Expanded Antiviral Pipeline with New Hepatitis E Virus (HEV) Program; Lead Product Candidate AT-587

Expected to Enter Clinic Mid-2026

Company Holding Conference Call Today at 4:30 PM ET

BOSTON, Mass., March 5, 2026 - Atea Pharmaceuticals, Inc. (Nasdaq: AVIR) (Atea or Company), a late-stage clinical

biopharmaceutical company engaged in the discovery and development of oral antiviral therapeutics for serious viral diseases, today reported financial results for the fourth quarter and full year ended December 31, 2025, and provided a business

"Our rigorous execution advancing our global Phase 3 HCV program and our unwavering resolve to address unmet clinical needs of patients

with serious viral diseases is driven by our core strength in discovering and developing oral antiviral treatments," said Jean-Pierre Sommadossi, PhD, Chief Executive Officer and Founder of Atea Pharmaceuticals. "In addition to

presenting new results reinforcing the potential best-in-class profile of our HCV regimen, engagements with key opinion leaders highlighted the unmet needs of current

HCV patients and their healthcare providers, and how our regimen is uniquely positioned to address them. We believe our regimen, if approved, has the ideal profile for the

test-and-treat model of care, to expand HCV treatment in the US and help advance global HCV eradication."

"In the year ahead, we remain focused on delivering topline results from our global Phase 3 HCV program and initiating clinical development of AT-587 for the treatment of HEV as we work to build a differentiated antiviral hepatitis franchise," continued Dr. Sommadossi.

Advanced Global Phase 3 Program for Potential Best-in-Class HCV Regimen with Strong Execution Setting the Stage for Topline Results in 2026

continues to advance its global Phase 3 program evaluating the fixed-dose combination (FDC) of bemnifosbuvir (BEM) and ruzasvir (RZR) for the treatment of chronic HCV. The global Phase 3 program consists of two open-label controlled trials: C-BEYOND in North America and C-FORWARD outside North America. In 2025, Atea advanced enrollment across both trials. The Company completed

C-BEYOND enrollment in December 2025 with over 880 patients and C-FORWARD is expected to complete enrollment mid-2026. C-BEYOND topline results are expected mid-2026 and C-FORWARD topline results are anticipated around

The primary endpoint for each trial is HCV RNA < lower limit of quantitation (LLOQ) at 24 weeks

from the start of treatment and encompasses sustained virologic response 12 weeks post-treatment (SVR12) in each arm. Measurement at 24 weeks from the start of treatment is to ensure the primary endpoint measurement occurs at the same relative

timepoint from the start of treatment in all patients. The primary endpoint will be assessed in the modified intent-to-treat population in

C-BEYOND and in the per-protocol population in C-FORWARD.

Last year, the Company presented several datasets supporting the potential

best-in-class profile of BEM/RZR, including results presented at the EASL Congress 2025 and The Liver Meeting

2025, the annual meeting of AASLD. Key data included:

In addition, recent data demonstrate a low risk of DDIs with proton pump

Atea also presented recent findings supporting a differentiated antiviral mechanism profile. BEM has an established mechanism of inhibition

of HCV RNA leading to chain termination, blocking viral production and replication inside the host cell. However, modeling of HCV viral kinetics from a Phase 1 study suggests that BEM may also inhibit the assembly/secretion of new HCV virions into

the bloodstream, significantly reducing extracellular HCV RNA. These findings may further explain the high antiviral potency of the regimen of BEM/RZR.

Physician Key Opinion Leaders (KOLs) Support Need for New HCV Treatment Optimized for

Test-and-Treat Model of Care

Last year, Atea hosted two dedicated

KOL events: a virtual panel in May featuring six physician leaders from US, Canada and EU, with expertise in hepatology, gastroenterology, infectious diseases and HCV treatments. The panel reviewed the Company's Phase 2 clinical trial results

and discussed what an optimized HCV treatment such as the BEM/RZR regimen could provide

for prescribers and patients. During another KOL event in November, which included a panel of four physicians with HCV expertise, the panel discussed current HCV treatment challenges, the value

of early diagnosis and treatment, and public policy initiatives including the test-and-treat model of care, along with what attributes are necessary for a novel therapy

to advance HCV disease eradication goals. The test-and-treat model of care reduces treatment barriers through rapid diagnosis and immediate initiation of treatment

following a positive HCV test result.

KOL viewpoints from discussions in these forums - combined with results from independent quantitative market

research conducted by IQVIA for the Company - underscored how the growing adoption of the test-and-treat model of care increases the need for HCV regimens with

profiles that combine high efficacy with practical, enhanced real-world usability. The KOLs noted how BEM/RZR fits this desired profile by offering a short treatment duration, low risk of DDIs and dosing convenience with no food effect.

Expanded Antiviral Pipeline with HEV Program, Advancing to Clinical Development Mid-2026

In late 2025, Atea announced the expansion of its antiviral pipeline into HEV. Atea identified two novel, proprietary development candidates, AT-587 and AT-2490, which showed potent nanomolar antiviral activity in vitro against HEV genotypes 1 and 3. The Company selected

AT-587 as the lead product candidate and anticipates that clinical development of AT-587 will begin in mid-2026 following the

completion of investigational new drug (IND)/clinical trial application (CTA) enabling studies.

Data Presented at CROI 2026 Support AT-587 as Potential First-in-Class Inhibitor for Treatment of HEV

Last month, Atea presented in vitro results showing the promising antiviral profiles of AT-587 and AT-2490 for the treatment of HEV infection, a single-stranded RNA virus that primarily infects liver cells, during the Conference on Retroviruses and Opportunistic Infections (CROI).

In vitro results demonstrated AT-587 - the lead product candidate for the Company's HEV program

- and AT-2490 were potent inhibitors of HEV replication. AT-587 and AT-2490 were 30-150-fold more potent against HEV compared with sofosbuvir and ribavirin. Analyses showed the two compounds were also active against other viruses, including all flaviviruses tested, rubella and

chikungunya. Antiviral activity of AT-587 and AT-2490 in the tissue of interest, human liver cells, was indicated by the formation of high amounts of active metabolite

of each compound. Neither compound showed any toxicity.

HEV, the causative agent of hepatitis E, is an increasing public health concern. In developing

regions waterborne transmission of genotypes 1 and 2 causes mostly acute self-limiting hepatitis. Conversely, in industrialized countries, especially in the US and Europe, foodborne transmission of predominantly genotype 3 causes chronic hepatitis

in immunocompromised patients, which can lead to cirrhosis in three to five years. There is a growing number of immunocompromised patients, a population that includes solid organ transplant and hematopoietic stem cell transplant recipients and

patients with hematologic malignancies such as multiple myeloma. Each year, in the US and Europe, 3% of the approximately 450,000 patients who have these underlying medical conditions are at risk of developing chronic HEV. There is currently no

approved antiviral therapy for HEV, and current off-label treatments have limited efficacy and tolerability, underscoring a clear and urgent unmet medical need.

Fourth Quarter and Full Year 2025 Financial Results

Cash and Investments: $301.8 million at December 31, 2025 compared to $454.7 million at December 31, 2024.

Research and Development Expenses: Research and development expenses were $47.8 million and $148.0 million for the fourth quarter and full

year 2025, respectively, compared to $25.7 million and $144.1 million for the corresponding periods in 2024. The net increase was partially driven by an increase in external spend for our HCV Phase 3 clinical development including the

purchase of comparator drug and expense related to the achievement of a milestone under the Merck License Agreement. The increase was partially offset by lower external spend related to the COVID-19 program

which was concluded in 2024 and lower internal research and development expenses primarily related to a decrease in stock-based compensation and payroll-related expense in the year ended December 31, 2025.

General and Administrative Expenses: General and administrative expenses were $7.1 million and $32.9 million for the fourth quarter and full

year ended December 31, 2025, respectively, compared to $13.4 and $48.8 million for the corresponding periods in 2024. The net decrease was primarily related to lower stock-based compensation expense, partially offset by increased

Interest Income and Other, Net: Interest income and other, net was $3.3 million and $16.4 million for the fourth

quarter and full year 2025, respectively, compared to $5.7 million and $25.5 million for the corresponding periods in 2024. The net decrease was primarily due to lower investment balances.

Income Taxes: We recorded an income tax benefit of $6.8 million and $6.2 million for the fourth quarter and full year ended December 31,

2025, respectively, compared to income tax expense of $0.2 million and $0.9 million for the corresponding periods in 2024. The net benefit was primarily the result of recognition of previously unrecognized tax benefits following a lapse in

the statute of limitations.

Condensed Consolidated Statement of Operations and Comprehensive Loss

(in thousands, except share and per share amounts)

Selected Condensed Consolidated Balance Sheet Data

Conference Call and Webcast

Atea will host a live

conference call and audio webcast today, Thursday, March 5, 2026, at 4:30 p.m. ET, to report financial results for the fourth quarter and full year 2025 ended December 31, 2025, and to provide a business update.

To access the live conference call, participants may register here. The live audio webcast of the call

will be available under "Events and Presentations" in the Investor Relations section of the Atea Pharmaceuticals website at ir.ateapharma.com. To participate via telephone, please dial 1-877-300-8521 (U.S.) or 1-412-317-6026

(International) and use conference ID number 10206566.

An archive of the audio webcast will be available on Atea's website approximately two hours

after the conference call ends and will remain available for at least 90 days following the event.

HCV is a blood-borne, positive-sense, single-stranded (ss) RNA virus that primarily infects liver cells. HCV is a leading cause of chronic liver disease and

liver transplants, spreading via blood transfusion, hemodialysis and needle sticks, with approximately 240,000 deaths occurring each year. Despite the availability of DAAs, HCV continues to be a significant global healthcare issue. An estimated

50 million people worldwide are chronically infected with HCV and there are approximately one million new infections each year. In the US, approximately four million people are estimated to have HCV with annual new infections outpacing

treatment rates. HCV infections in the US predominate in patients in the age group between 20 and 49 years old, and it is estimated that less than 10% of HCV-infected patients in the US have cirrhosis. Chronic

HCV infection is the leading cause of liver cancer in the US, Europe and Japan.

HEV is a positive-sense, single-stranded RNA virus which infects the liver and remains an under-recognized global health challenge with an estimated

20 million infections annually. Waterborne transmission of genotypes 1 and 2 causes mostly acute self-limiting hepatitis in developing regions, whereas foodborne transmission of genotype 3 predominates in the US and Europe and causes chronic

hepatitis in immunocompromised patients, which can lead to cirrhosis in three to five years. There is a growing number of immunocompromised patients, a population that includes solid organ transplant and hematopoietic stem cell transplant recipients

and patients with hematologic malignancies such as multiple myeloma. Each year, in the US and Europe, 3% of the approximately 450,000 patients who have these underlying medical conditions are at risk of developing chronic HEV. There is currently no

approved antiviral therapy for HEV, and current off-label treatments have limited efficacy and tolerability, underscoring a clear and urgent unmet medical need. Atea's initial HEV clinical efforts will

focus on developing AT-587 for the treatment of immunocompromised patients with chronic HEV.

Atea is a late-stage clinical biopharmaceutical company focused on discovering, developing and commercializing oral antiviral

therapies to address the unmet medical needs of patients with serious viral infections. Leveraging Atea's deep understanding of antiviral drug development, nucleos(t)ide chemistry, biology, biochemistry and virology, Atea has built a

proprietary nucleos(t)ide prodrug platform to develop novel product candidates to treat single-stranded ribonucleic acid, or ssRNA, viruses, which are a prevalent cause of serious viral diseases. Atea plans to continue to build its pipeline of

antiviral product candidates by augmenting its nucleos(t)ide platform with other classes of antivirals that may be used in combination with its nucleos(t)ide product candidates. Atea's Phase 3 program is evaluating the FDC regimen of BEM, a