Off to a good start

TARRYTOWN, NY—Regeneron Pharmaceuticals, Inc.'s Phase 3 trial of REGEN-COV has yielded encouraging results so far, the company announced this week. The trial is evaluating REGEN-COV—a casirivimab and imdevimab antibody cocktail—as a passive vaccine for preventing COVID-19 infection in those at high risk due to household exposure. Regeneron is jointly running the trial together with the National Institute of Allergy and Infectious Diseases, part of the NIH.

"These data using REGEN-COV as a passive vaccine suggest that it may both reduce transmission of the virus as well as reduce viral and disease burden in those who still get infected," said Dr. George D. Yancopoulos, president and chief scientific officer at Regeneron. "Even with the emerging availability of active vaccines, we continue to see hundreds of thousands of people infected daily, actively spreading the virus to their close contacts. The REGEN-COV antibody cocktail may be able to help break this chain by providing immediate passive immunity to those at high risk of infection, in contrast to active vaccines which take weeks to provide protection. There are also many individuals who unfortunately may be immunocompromised and not respond well to an active vaccine or are otherwise unable to be vaccinated, and REGEN-COV has the potential to be an important option for these individuals. Overall, the REGEN-COV development program has demonstrated definitive anti-viral activity, and the collective data strongly suggest it can be effective both as a therapeutic and as a passive vaccine."

This initial exploratory analysis looked at the first roughly 400 evaluable participants in the trial. The analysis found that passive vaccination with REGEN-COV led to 100-percent prevention of symptomatic infection and roughly 50-percent lower overall rates of infection (symptomatic and asymptomatic). The lower number of infections that occurred in the REGEN-COV arm of the trial were all asymptomatic and generally short-lived; infections reported in the REGEN-COV group lasted no more than a week, while roughly 40 percent of infections in the placebo cohort lasted between three and four weeks. In addition, those in the REGEN-COV group presented with lower peak virus levels and a shorter duration of viral shedding—44 total viral shedding weeks among the placebo group vs. nine weeks in the REGEN-COV, and 22 high viral shedding weeks (defined as >10^4 copies/mL) in placebo vs. 0 weeks in REGEN-COV.

Adverse events were recorded at 18 percent in the placebo group vs. 12 percent in the REGEN-COV group, with one COVID-19-related hospitalization and one death in the placebo group, and no COVID deaths or hospitalizations in the REGEN-COV group. Both groups saw injection site reactions at a rate of approximately 2 percent.

"In this prevention trial, REGEN-COV was given as injections rather than an infusion, which makes administration much more convenient and efficient for patients and overburdened healthcare providers and facilities," noted Dr. David Weinreich, Regenron's executive vice president and head of Global Clinical Development. "It's notable that the few infections that did occur after receiving REGEN-COV were all asymptomatic, and associated with markedly lower viral load and duration of viral shedding, potentially further reducing transmission. We look forward to seeing the full dataset early next quarter and will discuss the current results with regulatory authorities, including the potential to expand the Emergency Use Authorization."

The two antibodies that comprise REGEN-COV bind non-competitively to the critical receptor binding domain of the SARS-CoV-2 spike protein, which Regeneron notes “diminishes the ability of mutant viruses to escape treatment and protects against spike variants that have arisen in the human population.” The company also announced this week that it has been independently confirmed that REGEN-COV is capable of neutralizing the SARS-CoV-2 variants that were initially identified in the UK and South Africa. REGEN-COV was granted an Emergency Use Authorization (EUA) by the FDA in November for the treatment of individuals with mild or moderate COVID-19 who are not currently hospitalized but are at high risk of developing severe symptoms and requiring hospitalization. Regeneron has agreements in place with the US government to supply up to approximately 1.5 million doses of REGEN-COV under this EUA.