Trial met primary endpoint, showing REGEN-COV significantly reduced viral load within 7 days of treatment; trial conducted in patients hospitalized with COVID-19 who did not require high-flow oxygen or mechanical ventilation at baseline

Numeric improvements with REGEN-COV observed for all clinical endpoints, including a 36% reduced risk of death by day 29 in the overall population, increasing to 56% reduced risk in patients who were seronegative at baseline

Similar efficacy observed with both doses (2,400 mg and 8,000 mg); U.S. FDA is currently reviewing request to add treatment in hospital settings to REGEN-COV authorization

TARRYTOWN, NY, USA I September 30, 2021 I Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) today announced that a trial assessing investigational REGEN-COV™ (casirivimab and imdevimab) in patients hospitalized with COVID-19 met its primary endpoint. Trial results will be presented at IDWeek 2021 today, and show that REGEN-COV significantly reduced viral load in patients hospitalized with COVID-19 who entered the trial without having mounted their own antibody response (seronegative) and required low-flow or no supplemental oxygen (p=0.0172). The trial also had clinical results supportive of the much larger UK RECOVERY trial in hospitalized patients, with numeric improvements observed across all clinical endpoints assessed.

“COVID-19 continues to have a devastating impact on patients, our communities and healthcare systems, and has so far killed more than one in every 500 Americans,” said Eleftherios Mylonakis, M.D., Ph.D., primary investigator of the trial and Professor of Medicine, Molecular Microbiology and Immunology, and Director of Infectious Disease at Brown University and the Lifespan hospitals. “We need a multi-faceted approach to best manage the virus’ impact, including vaccination and effective treatment when patients become ill. These data show that REGEN-COV can benefit certain patients even after they are hospitalized, reducing the amount of virus and clinical consequences. Taken together with results announced earlier this year from the RECOVERY trial and other studies, these results have the potential to inform personalized care for hospitalized patients with this protean disease that presents with such high clinical variability.”

REGEN-COV is an investigational medicine authorized by the U.S. Food and Drug Administration (FDA) under an emergency use authorization to treat people who are at high risk of serious consequences from COVID-19 infection who are either already infected (non-hospitalized) or in certain post-exposure prophylaxis settings. In the U.S., it is not currently authorized in patients who are hospitalized due to COVID-19 infection.

The trial, which was stopped due to slow enrollment after recruiting just over one third the patients originally planned, found that patients who received REGEN-COV (2,400 mg or 8,000 mg) in addition to standard-of-care (SOC) experienced numeric improvements across all clinical endpoints assessed, compared to SOC alone (placebo). Researchers did not observe any clinical difference between the two REGEN-COV doses (2,400 mg or 8,000 mg), or any serious or dose-dependent safety signals in REGEN-COV treated patients. In a safety analysis involving 2,007 patients (REGEN-COV=1,340, placebo=667) serious adverse events occurred in 21% REGEN-COV patients (n=285) and 26% placebo patients (n=174). Infusion-related reactions and hypersensitivity reactions that were grade ≥2 occurred more commonly among REGEN-COV patients (2% and 1% respectively) than placebo patients (1% and <0.5% respectively). The trial originally assessed a broader group of patients; however in late 2020 the trial was adjusted to exclude patients who were on mechanical ventilation or high-flow oxygen at baseline based on a potential safety signal identified by an Independent Data Monitoring Committee in 199 patients on mechanical ventilation or high flow-oxygen, a finding that was not replicated in the much larger RECOVERY trial that enrolled hospitalized patients with a broad range of severe COVID-19, including these patient groups.

“These new results, combined with the nearly 10,000-patient RECOVERY trial, further validate how REGEN-COV can change the course of illness for patients even after they are hospitalized with COVID-19,” said George D. Yancopoulos, M.D., Ph.D., President and Chief Scientific Officer at Regeneron. “Patients who received REGEN-COV in this trial experienced a 36% reduced risk of dying within 29 days of receiving treatment, and in patients who were seronegative when they entered the trial the risk was reduced by 56%. It’s important to remember that while results from this and the RECOVERY trial indicate that patients unable to develop their own antibodies against COVID-19 historically had the poorest prognosis – and hence the greatest benefit from REGEN-COV treatment – both were largely conducted before widespread vaccination or the emergence of variants such as Delta. Consequently, serostatus may be less informative for treatment decisions in the future because it might not be practical to assess whether patients’ antibodies are for their current SARS-CoV-2 infection.”

The robust REGEN-COV development program has reported positive Phase 3 trial results across the spectrum of COVID-19 infection, from prevention to hospitalization:

  • Prevention of symptomatic infection in both uninfected and infected asymptomatic household contacts of SARS-CoV-2 infected individuals
  • Treatment of non-hospitalized patients already infected with SARS-CoV-2
  • Treatment of certain patients hospitalized due to COVID-19 infection (as detailed in the IDWeek presentation), including the RECOVERY trial

Multiple analyses have shown that the antibody cocktail retains potency against the main variants of concern circulating within the U.S., including Delta (first identified in India), Gamma (first identified in Brazil), Beta (first identified in South Africa) and Mu (first identified in Colombia), with information available in the Fact Sheet for Healthcare Providers. Consequently, REGEN-COV remains available for use across the U.S., and Regeneron will continue actively monitoring the potency of REGEN-COV against emerging variants. 

In the U.S., REGEN-COV is available for free to eligible people, as part of a U.S. government funded program and earlier this month Regeneron announced a new agreement with the U.S. government to supply an additional 1.4 million 1,200 mg doses of REGEN-COV. Information on how to access REGEN-COV throughout the U.S. is available from the Department of Health and Human Services and the National Infusion Center Association.  

The development and manufacturing of REGEN-COV have been funded in part with federal funds from the Biomedical Advanced Research and Development Authority, part of the U.S. Department of Health and Human Services’ Office of the Assistant Secretary for Preparedness and Response, under OT number: HHSO100201700020C.

About the Trial
The Phase 2/3, randomized, double-blind, placebo-controlled trial evaluated REGEN-COV in hospitalized adult patients with COVID-19. Of the 1,197 patients included in the efficacy analysis, 530 entered the trial with no supplemental oxygen and 667 were on low-flow oxygen. The safety analysis included results from all patients in the efficacy analysis plus additional patients from earlier stages of the clinical program who were on low-flow oxygen at baseline.

Patients were randomized 1:1:1 to receive a one-time infusion of REGEN-COV 8,000 mg, REGEN-COV 2,400 mg or placebo. All patients entering the trial were hospitalized with laboratory-confirmed COVID-19, and all received other background SOC as required including corticosteroids (75%) and remdesivir (55%).

On average, patients included in the efficacy analysis had experienced symptoms for 6 days prior to entering the trial, and nearly half (43%) were seronegative. Approximately 30% were Hispanic and 12% were African American. Patients were on average 62 years of age, 54% were male and 46% were female.

About the REGEN-COV Antibody Cocktail
REGEN-COV (casirivimab and imdevimab) is a cocktail of two monoclonal antibodies that was designed specifically to block infectivity of SARS-CoV-2, the virus that causes COVID-19, using Regeneron’s proprietary VelocImmune® and VelociSuite® technologies. The two potent, virus-neutralizing antibodies that form the cocktail bind non-competitively to the critical receptor binding domain of the virus’s spike protein, which diminishes the ability of mutant viruses to escape treatment and protects against spike variants that have arisen in the human population, as detailed in Cell and Science.

REGEN-COV has not been approved by the FDA, but is currently authorized in the U.S. for the treatment and post-exposure prophylaxis in certain high risk individuals. Post-exposure prophylaxis with REGEN-COV is not a substitute for vaccination against COVID-19. REGEN-COV is not authorized for pre-exposure prophylaxis for prevention of COVID-19 or for use in patients who are hospitalized due to COVID-19 or require oxygen therapy, or for people currently using chronic oxygen therapy because of an underlying comorbidity who require an increase in baseline oxygen flow rate due to COVID-19. This authorization is for the duration of the declaration that circumstances exist justifying the authorization of the emergency uses under section 564(b)(1) of the Act, 21 U.S.C. § 360bbb-3(b)(1), unless the authorization is terminated or revoked sooner. Additional information about REGEN-COV in the U.S. is below (authorized uses and important safety information).

In August, Regeneron submitted the first of two Biologics License Applications (BLAs) for REGEN-COV. The initial submission included data on the efficacy and safety of REGEN-COV to treat and prevent SARS-CoV-2 infection in non-hospitalized people. The second BLA submission will focus on those hospitalized because of COVID-19, and is expected to be completed later this year.  

Emergency or temporary pandemic use authorizations are currently in place in more than 40 countries, including the U.S., several European Union countries, India, Switzerland and Canada, and the antibody cocktail is fully approved in Japan and conditionally approved in the UK. 

Regeneron invented REGEN-COV and is collaborating with Roche to increase global supply, with Roche primarily responsible for development and distribution outside the U.S. Regeneron and Roche share a commitment to making the antibody cocktail available to COVID-19 patients around the globe and will support access in low- and lower-middle-income countries through drug donations to be made in partnership with public health organizations.

About Regeneron’s VelocImmune Technology
Regeneron’s VelocImmune technology utilizes a proprietary genetically engineered mouse platform endowed with a genetically humanized immune system to produce optimized fully human antibodies. When Regeneron’s President and Chief Scientific Officer George D. Yancopoulos was a graduate student with his mentor Frederick W. Alt in 1985, they were the first to envision making such a genetically humanized mouse, and Regeneron has spent decades inventing and developing VelocImmune and related VelociSuite technologies. Dr. Yancopoulos and his team have used VelocImmune technology to create approximately a quarter of all original, FDA-approved fully human monoclonal antibodies currently available. This includes REGEN–COV (casirivimab and imdevimab), Dupixent® (dupilumab), Libtayo® (cemiplimab-rwlc), Praluent® (alirocumab), Kevzara® (sarilumab), Evkeeza® (evinacumab-dgnb) and Inmazeb™ (atoltivimab, maftivimab and odesivimab-ebgn).


REGEN-COV is authorized for the treatment of mild to moderate coronavirus disease 2019 (COVID-19) in adults and pediatric patients (12 years of age and older weighing at least 40 kg) with positive results of direct SARS-CoV-2 viral testing, and who are at high risk for progression to severe COVID-19, including hospitalization or death

Limitations of Authorized Use (Treatment)

  • REGEN-COV is not authorized for use in patients:
    • who are hospitalized due to COVID-19, OR
    • who require oxygen therapy due to COVID-19, OR
    • who require an increase in baseline oxygen flow rate due to COVID-19 in those on chronic oxygen therapy due to underlying non-COVID-19 related comorbidity
  • Monoclonal antibodies, such as REGEN-COV, may be associated with worse clinical outcomes when administered to hospitalized patients with COVID-19 requiring high-flow oxygen or mechanical ventilation

Post-Exposure Prophylaxis:
REGEN-COV is authorized in adult and pediatric individuals (12 years of age and older weighing at least 40 kg) for post-exposure prophylaxis of COVID-19 in individuals who are at high risk for progression to severe COVID-19, including hospitalization or death, and are:

  • not fully vaccinated or who are not expected to mount an adequate immune response to complete SARS-CoV-2 vaccination (for example, individuals with immunocompromising conditions including those taking immunosuppressive medications) and
    • have been exposed to an individual infected with SARS-CoV-2 consistent with close contact criteria per Centers for Disease Control and Prevention (CDC) or
    • who are at high risk of exposure to an individual infected with SARS-CoV-2 because of occurrence of SARS-CoV-2 infection in other individuals in the same institutional setting (for example, nursing homes, prisons)

Limitations of Authorized Use (Post-Exposure Prophylaxis)

  • Post-exposure prophylaxis with REGEN-COV is not a substitute for vaccination against COVID-19
  • REGEN-COV is not authorized for pre-exposure prophylaxis for prevention of COVID-19

REGEN-COV has not been approved, but has been authorized for emergency use by FDA

These uses are authorized only for the duration of the declaration that circumstances exist justifying the authorization of the emergency use under section 564(b)(1) of the Act, 21 U.S.C. § 360bbb-3(b)(1), unless the authorization is terminated or revoked sooner

Healthcare providers should review the Fact Sheet for Healthcare Providers for information on the authorized uses of REGEN-COV and mandatory requirements of the EUA and must comply with the requirements of the EUA. The FDA Letter of Authorization is available for reference, as well as the Dear Healthcare Provider Letter and Patient Fact Sheet

Criteria for Identifying High Risk Individuals

Please refer to the Fact Sheet for Healthcare Providers for criteria for identifying high risk individuals

SARS-CoV-2 Viral Variants

Circulating SARS-CoV-2 viral variants may be associated with resistance to monoclonal antibodies. Healthcare providers should review the Antiviral Resistance information in Section 15 of the Fact Sheet for details regarding specific variants and resistance, and refer to the CDC website ( as well as information from state and local health authorities regarding reports of viral variants of importance in their region to guide treatment decisions

About Regeneron
Regeneron (NASDAQ: REGN) is a leading biotechnology company that invents life-transforming medicines for people with serious diseases. Founded and led for over 30 years by physician-scientists, our unique ability to repeatedly and consistently translate science into medicine has led to nine FDA-approved treatments and numerous product candidates in development, almost all 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, pain, hematologic conditions, infectious diseases and rare diseases.

Regeneron is accelerating and improving the traditional drug development process through our proprietary VelociSuite technologies, such as VelocImmune, which uses unique genetically humanized mice to produce optimized fully human antibodies and bispecific antibodies, and through ambitious research initiatives such as the Regeneron Genetics Center, which is conducting one of the largest genetics sequencing efforts in the world.

For additional information about the company, please visit or follow @Regeneron on Twitter.

SOURCE: Regeneron Pharmaceuticals