Inmazeb^® (a three-antibody cocktail consisting of maftivimab, atoltivimab and odesivimab-ebgn) was the first Ebola treatment approved by the U.S. Food and Drug Administration, indicated specifically for the Orthoebolavirus zairense species, and has been administered to hundreds of patients

Maftivimab, the most potent neutralizing antibody in Inmazeb, has shown broad activity in vitro against multiple Ebola species, including Bundibugyo

Maftivimab has been recommended to be studied as a monotherapy in the current outbreak

TARRYTOWN, N.Y., May 28, 2026 (GLOBE NEWSWIRE) -- Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) today announced that maftivimab, the most potent neutralizing antibody included in Inmazeb^® (maftivimab, atoltivimab and odesivimab-ebgn), has been recommended by the World Health Organization's (WHO) Therapeutics Advisory Group to be prioritized for evaluation in clinical trials of investigational treatments for Bundibugyo ebolavirus. Maftivimab has demonstrated broad activity in vitro against multiple Ebola species, including Bundibugyo.

The trial pertains to the WHO's recent declaration that the current outbreak of Ebola disease caused by Bundibugyo virus in the Democratic Republic of the Congo (DRC) and Uganda constitutes a public health emergency of international concern. WHO is now working closely with the governments of DRC and Uganda to facilitate the implementation of research evaluations of the prioritized products.

"We are closely coordinating our efforts with the U.S. Department of Health and Human Services (HHS) and look forward to working with the World Health Organization and others as clinical evaluation moves ahead," said Leonard S. Schleifer, M.D., Ph.D., Board co-Chair, President and Chief Executive Officer of Regeneron. "Regeneron has a track record of rapidly delivering important medical solutions during times of global health crisis, such as the COVID-19 pandemic and multiple Ebola outbreaks, and we know that independently run and locally executed clinical trials are critical to developing effective new medicines in such situations."

Inmazeb is already approved by the U.S. Food and Drug Administration for the treatment of infection caused by Orthoebolavirus zairense, also known as Zaire ebolavirus, in adult and pediatric patients, including neonates born to infected mothers. Maftivimab is the most potent virus-neutralizing component of Inmazeb and has demonstrated broad neutralizing activity in laboratory studies against Bundibugyo ebolavirus; it has not yet been tested in vivo as a monotherapy against this distinct Ebola virus. Maftivimab has been administered to hundreds of human patients as a component of Inmazeb, which has demonstrated an acceptable safety profile. Since 2018, Inmazeb has been offered by Regeneron at no cost under a compassionate use protocol to infected persons in countries experiencing an Orthoebolavirus zairense outbreak, including the DRC and Guinea.

"Regeneron's prior work in Ebola has shown how innovative science and groundbreaking technology platforms can be rapidly translated into life-saving medicines for people facing some of the world's most dangerous infectious diseases," said George D. Yancopoulos, M.D., Ph.D., Board co-Chair, President and Chief Scientific Officer of Regeneron. "As we advance our robust portfolio of transformative medicines, we always strive to do the right thing when patients and the world need urgent scientific action – whether that's by collaborating with global health organizations to pursue new treatments or offering a life-changing new gene therapy for free in the United States."

In September 2025, the company donated 500 doses of Inmazeb to the WHO for exclusive use by governments of low- and lower-middle income countries that are most at-risk for Ebola outbreaks.¹ Regeneron has also delivered a stockpile of Inmazeb to the U.S. Government as part of HHS's efforts to enhance national preparedness for public health emergencies. The company is closely coordinating its response efforts with the United States Government.

Regeneron is working as quickly as possible to prepare existing supply of maftivimab for use in potential upcoming clinical trials. Supply of Inmazeb is already on the ground in the DRC, should WHO wish to utilize it for immediate treatment or as an additional component of the study. Regeneron is also supporting Afya Foundation's emergency response efforts aimed at safeguarding frontline healthcare workers and strengthening healthcare system resilience during the current outbreak.

About Inmazeb

Inmazeb is approved by the U.S. FDA for the treatment of infection caused by Orthoebolavirus zairense (also known as Zaire ebolavirus) in adult and pediatric patients, including neonates born to a mother who is RT-PCR positive for Orthoebolavirus zairense infection.

Inmazeb was created using Regeneron's VelocImmune^® platform and associated VelociSuite^®technologies. The treatment consists of three monoclonal antibodies that help neutralize the Ebola virus by blocking its ability to invade a patient's cells and/or enlisting other immune cells to target infected cells and remove them from the body.

The safety and efficacy of Inmazeb was established through the 681-patient PALM Trial, which was independently conducted by the WHO, the National Institutes of Health (NIH) and the Institut National de Recherche Biomédicale (INRB) during the 2018 DRC outbreak. In 2019, as reported in the New England Journal of Medicine, the PALM Trial was stopped early following a pre-specified interim analysis that showed the superiority of Inmazeb in preventing death versus two other investigational treatments.

Inmazeb was approved by the FDA in 2020, and in 2022, WHO published its first guidelines for Ebola virus therapeutics, which strongly recommends the use of Inmazeb for treatment of Zaire ebolavirus infection and calls on the global community to engage all possible mechanisms to improve access to life-saving Ebola medicines. Heeding this call, in November 2023, Inmazeb became the first and only Ebola treatment to be prequalified by the WHO, certifying that the medicine meets WHO's standards for quality, safety and efficacy and is considered "essential." In addition to the supply channels established in the U.S. and low- and lower-middle income countries, Regeneron has also worked with governments in higher- and middle-income countries to establish Inmazeb stockpiles.

Inmazeb was developed in collaboration and with federal funds from BARDA, part of the Office of the Assistant Secretary for Preparedness and Response at the HHS under ongoing USG Contract Nos. HHSO100201700016C and HHSO100201500013C.

IMPORTANT SAFETY INFORMATION AND INDICATION

WARNINGS AND PRECAUTIONS

Hypersensitivity Reactions Including Infusion-Associated Events: Hypersensitivity reactions including infusion-associated events have been reported during and post-infusion with INMAZEB. These may include acute, life-threatening reactions during and after the infusion. Monitor all patients for signs and symptoms including, but not limited to, hypotension, chills and elevation of fever, during and following INMAZEB infusion. In the case of severe or life-threatening hypersensitivity reactions, discontinue the administration of INMAZEB immediately and administer appropriate emergency care.

Infusion could not be completed in 1% of subjects who received INMAZEB due to infusion-associated adverse events. The rate of infusion of INMAZEB may be slowed or interrupted if the patient develops any signs of infusion-associated events or other adverse events.

ADVERSE REACTIONS: The most common adverse events reported in at least 20% of subjects who received INMAZEB were pyrexia (or elevation in fever), chills, tachycardia, tachypnea and vomiting. The evaluation of adverse events in subjects who received INMAZEB may have been confounded by the signs and symptoms of the underlying Orthoebolavirus zairense infection.

DRUG INTERACTIONS: INMAZEB may reduce the efficacy of live vaccine therefore, avoid the concurrent administration of a live vaccine during treatment with INMAZEB. The interval between live vaccination following initiation of INMAZEB therapy should be in accordance with current vaccination guidelines. The efficacy of INMAZEB among subjects who reported receipt of a recombinant live vaccine prior to their enrollment in the PALM clinical trial was similar to subjects who did not receive a vaccine.

INDICATION

INMAZEB is indicated for the treatment of infection caused by Orthoebolavirus zairense in adult and pediatric patients, including neonates born to a mother who is RT-PCR positive for Orthoebolavirus zairense infection.

Limitations of Use: The efficacy of INMAZEB has not been established for other species of the Orthoebolavirus and Orthomarburgvirus genera. Orthoebolavirus zairense can change over time, and factors such as emergence of resistance, or changes in viral virulence could diminish the clinical benefit of antiviral drugs. Consider available information on drug susceptibility patterns for circulating Orthoebolavirus zairense strains when deciding to use INMAZEB.

Please see accompanying full Prescribing Information.

About Regeneron

Regeneron (NASDAQ:REGN) is a leading biotechnology company that invents, develops and commercializes life-transforming medicines for people with serious diseases. Founded and led by physician-scientists, our unique ability to repeatedly and consistently translate science into medicine has led to numerous approved treatments and product candidates in development, most of which were homegrown in our laboratories. Our medicines and pipeline are designed to help patients with eye diseases, allergic and inflammatory diseases, cancer, cardiovascular and metabolic diseases, neurological diseases, hematologic conditions, infectious diseases, and rare diseases.

Regeneron pushes the boundaries of scientific discovery and accelerates drug development using our proprietary technologies, such as VelociSuite^®, which produces optimized fully human antibodies and new classes of bispecific antibodies. We are shaping the next frontier of medicine with data-powered insights from the Regeneron Genetics Center^® and pioneering genetic medicine platforms, enabling us to identify innovative targets and complementary approaches to potentially treat or cure diseases.

For more information, please visit www.Regeneron.com or follow Regeneron on LinkedIn, Instagram, Facebook or X.

Forward-Looking Statements and Use of Digital Media

This press release includes forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Regeneron Pharmaceuticals, Inc. ("Regeneron" or the "Company"), and actual events or results may differ materially from these forward-looking statements. Words such as "anticipate," "expect," "intend," "plan," "believe," "seek," "estimate," variations of such words, and similar expressions are intended to identify such forward-looking statements, although not all forward-looking statements contain these identifying words. These statements concern, and these risks and uncertainties include, among others, the nature, timing, and possible success and therapeutic applications of products marketed or otherwise commercialized by Regeneron and/or its collaborators or licensees (collectively, "Regeneron's Products") and product candidates being developed by Regeneron and/or its collaborators or licensees (collectively, "Regeneron's Product Candidates") and research and clinical programs now underway or planned, including without limitation Inmazeb^® (maftivimab, atoltivimab and odesivimab-ebgn) and maftivimab (an antibody included in Inmazeb); the likelihood, timing, and scope of possible regulatory approval and commercial launch of Regeneron's Product Candidates and new indications for Regeneron's Products, such as maftivimab for the treatment of Bundibugyo ebolavirus as discussed in this press release; uncertainty of the utilization, market acceptance, and/or commercial success of Regeneron's Products and Regeneron's Product Candidates and the impact of studies (whether conducted by Regeneron or others and whether mandated or voluntary), including the studies discussed or referenced in this press release, on any of the foregoing or any potential regulatory approval of Regeneron's Products and Regeneron's Product Candidates (such as maftivimab); the impact of public health outbreaks, epidemics, or pandemics on Regeneron's business (including the current Bundibugyo ebolavirus outbreak referenced in this press release); the ability of Regeneron's collaborators, licensees, suppliers, or other third parties (as applicable) to perform manufacturing, filling, finishing, packaging, labeling, distribution, and other steps related to Regeneron's Products and Regeneron's Product Candidates; the ability of Regeneron to manage supply chains for multiple products and product candidates and risks associated with tariffs and other trade restrictions; safety issues resulting from the administration of Regeneron's Products and Regeneron's Product Candidates (such as maftivimab) in patients, including serious complications or side effects in connection with the use of Regeneron's Products and Regeneron's Product Candidates in clinical trials; determinations by regulatory and administrative governmental authorities which may delay or restrict Regeneron's ability to continue to develop or commercialize Regeneron's Products and Regeneron's Product Candidates; ongoing regulatory obligations and oversight impacting Regeneron's Products, research and clinical programs, and business, including those relating to patient privacy; the availability and extent of reimbursement or copay assistance for Regeneron's Products from third-party payors and other third parties, including private payor healthcare and insurance programs, health maintenance organizations, pharmacy benefit management companies, and government programs such as Medicare and Medicaid; coverage and reimbursement determinations by such payors and other third parties and new policies and procedures adopted by such payors and other third parties; changes to drug pricing regulations and requirements and Regeneron's pricing strategy, including in connection with Regeneron's April 2026 agreements with the U.S. government; other changes in laws, regulations, and policies affecting the healthcare industry; competing products and product candidates (including biosimilar products) that may be superior to, or more cost effective than, Regeneron's Products and Regeneron's Product Candidates; the extent to which the results from the research and development programs conducted by Regeneron and/or its collaborators or licensees may be replicated in other studies and/or lead to advancement of product candidates to clinical trials, therapeutic applications, or regulatory approval; unanticipated expenses; the costs of developing, producing, and selling products; the ability of Regeneron to meet any of its financial projections or guidance and changes to the assumptions underlying those projections or guidance; the potential for any license, collaboration, or supply agreement, including Regeneron's agreements with Sanofi and Bayer (or their respective affiliated companies, as applicable), to be cancelled or terminated; and risks associated with litigation and other proceedings and government investigations relating to the Company and/or its operations (including the pending civil proceedings initiated or joined by the U.S. Department of Justice and the U.S. Attorney's Office for the District of Massachusetts), risks associated with intellectual property of other parties and pending or future litigation relating thereto (including without limitation the patent litigation and other related proceedings relating to EYLEA^® (aflibercept) Injection), the ultimate outcome of any such proceedings and investigations, and the impact any of the foregoing may have on Regeneron's business, prospects, operating results, and financial condition. A more complete description of these and other material risks can be found in Regeneron's filings with the U.S. Securities and Exchange Commission, including its Form 10-K for the year ended December 31, 2025 and its Form 10-Q for the quarterly period ended March 31, 2026. Any forward-looking statements are made based on management's current beliefs and judgment, and the reader is cautioned not to rely on any forward-looking statements made by Regeneron. Regeneron does not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

Regeneron uses its media and investor relations website and social media outlets to publish important information about the Company, including information that may be deemed material to investors. Financial and other information about Regeneron is routinely posted and is accessible on Regeneron's media and investor relations website (https://investor.regeneron.com) and its LinkedIn page (https://www.linkedin.com/company/regeneron-pharmaceuticals).

Regeneron Contacts:

Media Relations

Alexandra Bowie

Tel: +1 (914) 847-3407

Alexandra.Bowie@regeneron.com

Investor Relations

Mark Hudson

Tel: +1 914-847-5443

mark.hudson@regeneron.com

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¹ As defined by the World Bank based on gross national income per capita.

Regeneron's Ebola Antibody Recommended by World Health Organization for Investigational Use in Response to Current Bundibugyo Ebolavirus Outbreak