- Results from a phase 3 clinical trial show that Regeneron’s antibody cocktail has the ability to cut the risk of COVID-19 hospitalization and death by 70 percent.
- The treatment also shortened the duration of COVID-19 symptoms by 4 days.
- The two antibodies work similarly to the antibodies the immune system naturally produces to fight the coronavirus.
Regeneron’s monoclonal antibody drug treatment can reduce COVID-19 hospitalization and death by 70 percent, according to a press release published March 23.
The treatment also reduced the length of COVID-19 symptoms by 4 days, on average.
All Regeneron doses that were tested — 8,000 milligrams (mg), 2,400 mg, and 1,200 mg — were similarly effective.
Regeneron originally planned to have 750,000 doses available by June. If the lower doses are approved for use, the company could potentially produce 1.25 million by then.
The treatment was given to former President Donald Trump shortly after he contracted the coronavirus in October 2020. Trump’s condition improved soon after receiving the treatment.
Treatment significantly improves outcomes from COVID-19
The new findings come from Regeneron’s phase 3 trial, which is the largest clinical trial to date that has evaluated a COVID-19 treatment in people who have COVID-19 but aren't hospitalized.
The trial included 4,567 people who recently developed COVID-19 and were high risk for severe illness.
The 2,400-mg dose reportedly cut the risk of hospitalization and death by 71 percent. The 1,200-mg dose cut the risk of hospitalization by 70 percent.
Regeneron plans to request the Food and Drug Administration to approve the lower dosage, which could help ramp up supply.
The antibody combination also shortened the duration of symptoms by 4 days, on average.
It wasn't given to people hospitalized for COVID-19. Some monoclonal antibody treatments have been associated with worse outcomes when given to people hospitalized for COVID-19 who require oxygen or mechanical ventilation.
How does the Regeneron treatment work?
The treatment contains two neutralizing antibody drugs, casirivimab and imdevimab. It's administered through a vein.
The two antibodies work similarly to the antibodies the immune system naturally produces to fight the coronavirus.
“These antibodies last for a short period of time and do not provide long-term antibody protection,” Powell said.
By fighting the virus’s ability to bind to our cells, the antibody treatment can improve COVID-19 symptoms and prevent the disease from worsening.
The treatment works best when given earlier in the course of disease, ideally within 10 days after symptoms develop.
“The idea is to stop the virus before it even becomes a problem,” said Dr. Melissa Fiorini, an emergency medicine physician at St. Peter's Hospital in New York.
The drug is intended for people who are at risk for hospitalization or death.
At the first sight of symptoms, Fiorini said people with high risk for severe COVID-19 should get tested and treated as soon as possible.
Could variants resist the monoclonal antibodies?
Potentially. Certain variants have diminished the effectiveness of other monoclonal antibodies.
The findings published by Regeneron on March 23 state that “circulating SARS-CoV-2 viral variants may be associated with resistance to monoclonal antibodies.”
The monoclonal antibodies are designed to neutralize the spike protein, which is where many of the variants’ mutations exist.
Early evidence suggests Regeneron’s antibody treatment retained its potent neutralizing capability against variants.
Laboratory tests have found that Regeneron’s antibody treatment holds up against variants, including the B.1.1.7 variant first detected in the United Kingdom and the B.1.351 variant first identified in South Africa.
“Imdevimab retained its potency against this variant [B.1.351], and while casirivimab potency was reduced, it was still comparable to the potency that other single antibodies in development have against the original virus,” Powell said.
The variant detected in Brazil, called 1.1.248, has the same mutations as the B.1.351 variant, so the Regeneron treatment is expected to remain similarly effective, according to Powell.
Fiorini said it’s unclear how in vitro findings will compare with clinical disease.
Regeneron is continuing to test the treatment against variants, including the variant detected in Brazil.
The bottom line
Results from a phase 3 clinical trial show that Regeneron’s COVID-19 antibody treatment has the ability to cut the risk of hospitalization and death by 70 percent.
The treatment also shortened the duration of COVID-19 symptoms by 4 days.
The two antibodies included in the treatment work similarly to the antibodies the immune system naturally produces to fight the coronavirus.