Regeneron’s Antibody Cocktail Shows Success in Preventing COVID-19 in Phase 3 Study

In what looks like a breakthrough for COVID-19 treatments, Regeneron’s monoclonal antibody cocktail REGEN-COV (casirivimab and imdevimab) cut infection rates in half and provided full protection against symptomatic COVID-19, according to interim results from a phase 3 trial evaluating the treatment as a passive vaccine.

The early analysis is from a National Institutes of Health- (NIH) supported trial in 409 participants. They were not infected at baseline, had no existing SARS-CoV-2 antibodies in their blood and were living with an infected person. Researchers found that the cocktail prevented symptomatic infection in all 186 participants who were given a 1,200-mg injected dose, compared to eight of 223 placebo patients who developed symptoms.

The cocktail, which is already cleared under FDA Emergency Use Authorization (EUA) for treating high-risk patients with mild-to-moderate COVID-19 symptoms (DID, Nov. 24, 2020), also provided an approximately 50 percent reduction in infection rates. And the infections that did occur in the REGEN-COV group were asymptomatic, did not have high viral loads and lasted no longer than a week. Infections in the placebo group lasted three to four weeks and had a 100-fold higher viral load on average.

Regeneron believes that the results could support emergency clearance of the treatment as a passive vaccine, which directly delivers antibodies into the body that combat the virus, compared to conventional vaccines that teach the immune system to make antibodies to the virus.

Full data from the phase 3 trial is expected early in the second quarter, but in the meantime, the company said it will discuss the interim results with regulators, including the FDA, and inquire about expanding its EUA.

“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,” said George Yancopoulos, Regeneron’s president and chief scientific officer. “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.”

The interim results have not yet undergone peer-review or been published in an academic journal. The trial is currently ongoing and has enrolled more than 2,000 participants.

Eli Lilly has also announced positive phase 3 results for its antibody cocktail, which is comprised of the monoclonal antibodies bamlanivimab (LY-CoV555) and etesevimab (LY-CoV016). The late-stage trial met both its primary and key secondary endpoints with high statistical significance, the company said. The cocktail, which the FDA is still reviewing as an emergency treatment for mild-to-moderate COVID-19 in high-risk patients, reduced deaths and hospitalizations in high-risk, recently diagnosed patients by 70 percent. Of the 1,035 patients in the trial, 10 deaths were seen in the placebo group while none were seen in patients given the cocktail, the drugmaker said.

“These exciting results, which replicate positive phase 2 data in a much larger set of patients, add valuable clinical evidence about the role neutralizing antibodies can play in fighting this pandemic," said Daniel Skovronsky, Eli Lilly’s chief scientific officer and president of Lilly Research Laboratories.

“These [phase 3] data further support our belief that bamlanivimab and etesevimab together have the potential to be an important treatment that significantly reduces hospitalizations and death in high-risk COVID-19 patients,” he said.

So far, only bamlanivimab has received an EUA for treating high-risk patients with mild-to- moderate COVID-19. — James Miessler