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Data from a phase 3 clinical trial for REGEN-COV, a combination monoclonal antibody therapy (casirivimab with imdevimab), is part of the NIH-sponsored COVID Prevention Network, co-led by Myron Cohen at UNC-Chapel Hill.

Regeneron Pharmaceuticals, Inc. announced positive data from a phase 3 trial of recently infected asymptomatic COVID-19 patients, evaluating REGEN-COV™ (casirivimab with imdevimab) 1,200 mg administered via injection. REGEN-COV reduced the overall risk of progressing to symptomatic COVID-19 by 31% and by 76% after the third day. The trial also demonstrated that REGEN-COV shortened symptom duration, markedly reduced viral levels, and reduced the risk of spreading the infection within individual households.

The phase 3 trial, jointly run with the National Institute of Allergy and Infectious Diseases (NIAID), enrolled 204 individuals without any COVID-19 symptoms who tested positive for SARS-CoV-2 but did not have anti-virus antibodies at baseline, and were randomized to receive either one dose of REGEN-COV (1,200 mg) or placebo.

“COVID-19 transmission often occurs via infected people who do not yet have symptoms, so it is critical that we rapidly diagnose and treat these individuals for their own health and to prevent transmission,” said Katharine Bar, MD, co-principal investigator of the trial and assistant professor of medicine at the University of Pennsylvania. “These data pave the way for REGEN-COV to be used before patients become symptomatic, with a more convenient subcutaneous administration.”

The trial met all primary and key secondary endpoints. In addition to reducing the risk of symptomatic infections, the total number of weeks patients experienced symptoms was nearly cut in half (45%) with REGEN-COV, and the viral burden was reduced by more than 90%. While not included in the initial analysis plan, researchers also found that no REGEN-COV patients and 6 placebo patients were either hospitalized or visited the emergency room because of COVID-19 during the 29-day efficacy assessment period.

The data build on previously announced results from the phase 3 outcomes and Phase 2 virology trials in non-hospitalized COVID-19 patients. The phase 3 outcomes trial in high-risk symptomatic outpatients showed that REGEN-COV reduced hospitalization or death by 70%. The Phase 2 virology trial in low-risk outpatients showed that all REGEN-COV doses studied had similar efficacy in rapidly reducing viral load.

Phase 3 trial results also showed that REGEN-COV reduced the risk of symptomatic infections by 81% in household contacts of COVID-19 patients.

“These data suggest that REGEN-COV can complement widespread vaccination strategies, particularly for those at high risk of infection. Importantly, to date REGEN-COV has been shown in vitro to retain its potency against emerging COVID-19 variants of concern,” said Myron Cohen, MD, director of the UNC Institute for Global Health and Infectious Diseases and leader of the monoclonal antibody efforts for the COVID Prevention Network. “Despite standard precautions to reduce transmission, nearly 10% of unvaccinated individuals living with an infected person developed symptomatic infections if they did not receive REGEN-COV. If authorized, convenient subcutaneous administration of REGEN-COV could help control outbreaks in high-risk settings where individuals have not yet been vaccinated, including individual households and group living settings.”

Learn more about monoclonal antibody treatment available throughout the UNC Health System.