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When REGEN-COV treatment is administered, it can provide a “passive immunity” by limiting the ability of the coronavirus to develop into a symptomatic illness. Michael Nagle/Bloomberg via Getty Images
  • Last spring, a study found that REGEN-COV, a monoclonal antibody drug, can reduce the risk of coronavirus transmission by 81 percent.
  • Now new evidence finds that the treatment is likely not effective against the Omicron variant.
  • Experts say the treatment still works against Delta.

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Last April, drugmaker Regeneron Pharmaceuticals announced in a press release that one injection of its monoclonal antibody drug reduced the infection risk of volunteers exposed to the coronavirus by 81 percent.

This was a phase 3, double-blind, placebo-controlled trial. It was jointly run by the National Institute of Allergy and Infectious Diseases (NIAID).

But now new variants of the coronavirus mean this drug’s effectiveness is in doubt.

On November 30, 2022, the Food and Drug Administration (FDA) deauthorized bebtelovimab for emergency use in the United States. This was the last monoclonal antibody drug authorized by the FDA to treat COVID-19. The decision was made because it is not expected to neutralize new Omicron subvariants.

While Regeneron confirmed in a recent press release that multiple “next generation” monoclonal antibodies that target the coronavirus are active against Omicron, the company also admitted the treatment may not be fully effective against this new variant.

“While Regeneron’s currently authorized REGEN-COV antibodies have diminished potency against Omicron, they are active against Delta, which currently is the most prevalent variant in the U.S.,” wrote the drugmaker.

However, on Dec. 16, AstraZeneca announced that its Evusheld antibody treatment was found effective against Omicron, according to preliminary data from an independent Food and Drug Administration (FDA) study.

According to AstraZeneca, these findings “add to the growing body of preclinical evidence demonstrating that Evusheld retains activity against all tested variants of concern to date.”

According to Regeneron, the April clinical trial assessed the effect of REGEN-COV on more than 1,500 participants who did not have a coronavirus infection, coronavirus antibodies, or any COVID-19 symptoms.

These participants shared the same household as someone who tested positive for the coronavirus within the prior 4 days.

Participants were randomized to be given either one 1,200-milligram dose of REGEN-COV or a placebo, administered by injection.

“These findings are very encouraging and suggest that REGEN-COV is highly effective at preventing symptomatic COVID-19 in household contacts of SARS-CoV-2 infected individuals,” said Dr. Dan H. Barouch, co-principal investigator of the trial and director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, in a statement.

According to Dr. Sean Liu, medical director of the Mount Sinai COVID Clinical Trials Unit, intravenous (IV) infusions require specialized facilities and commonly require several hours to complete a single visit compared to the single injection from Regeneron.

Liu explained in an earlier interview that when administered, REGEN-COV provides a “passive immunity” by limiting the ability of the coronavirus to develop into a symptomatic illness.

Liu emphasized the drug is meant to preemptively treat people who have been exposed to the virus, not people who already have COVID-19.

“REGEN-COV is given during a one-time visit as four subcutaneous injections to healthy persons who have not been diagnosed with COVID-19 but who have had a significant exposure to COVID-19. For example, a household member recently becomes infected with COVID-19,” Liu told Healthline.

Joan Kapusnik-Uner, PharmD, vice president of clinical content at First Databank, a provider of integrated drug and medical device databases, explained that monoclonal antibodies are manufactured antibodies very much like those the human immune system would make after a viral infection.

“Administering more than one type of monoclonal antibody in a combination, a so-called ‘cocktail,’ increases the chance that a viral infection with SARS-CoV-2 will be prevented from worsening,” she explained.

“Said another way, two drugs, also known as monoclonal antibodies, given together are better than one for treating COVID-19,” she continued.

Kapusnik-Uner added that coronavirus variants that are becoming known are also better treated with this drug combination.

“This is great preliminary news regarding efficacy data for the subcutaneous route of administration (injection) of Regeneron’s antibody cocktail, casirivimab plus imdevimab,” Kapusnik-Uner said.

She added that while IV infusions may, infrequently, cause adverse effects in 1 to 2 percent of people, the injection could have a similar or better safety profile.

“But it is really the improved logistics that make this new option so exciting,” she said.

According to Kapusnik-Uner, this new preliminary study data and others show that we need to continue to increase access to monoclonal antibody cocktails.

“The adage of ‘the sooner the better’ seems to hold true for this antibody cocktail — whether for newly diagnosed COVID-positive patients who are high-risk patients where it prevents hospitalization, morbidity, and mortality, or for the new primary prophylaxis,” she said.

“We need to continue to raise awareness that these types of antibody cocktails, from both Regeneron and Eli Lilly, are available and are very effective treatments in high-risk patients when given early on in an infection to halt disease progression,” Kapusnik-Uner said.

She also said that access to monoclonal antibody treatments “via outpatient infusion centers or mobile services exists,” but they may be unavailable in certain locations due to logistical barriers.

“Complicating things further is the fact that outpatient infusion centers may also be providing services to oncology (cancer) patients, who should not come in contact with COVID-positive patients seeking antibody therapy,” she said.

Kapusnik-Uner believes that this new subcutaneous therapy option will really improve overall access, and she looks forward to seeing Regeneron’s new data published.