A Covid-19 antibody cocktail developed by Regeneron Pharmaceuticals and Roche has pivotal clinical trial data showing it protected against the spread of infection among people in the same household. The results support use of the drug as a preventative measure in a formulation that’s easier for both physicians and patients.

In the placebo-controlled Phase 3 test, which was conducted with the National Institutes of Health, the main goal was to show a reduction in the risk of symptomatic Covid infection in uninfected people. The antibody cocktail met that goal, reducing the infection risk by 81%. With the data, Regeneron and Roche said that they would seek to expand U.S. and European authorizations for the antibody to include disease prevention.

While the efficacy results are important, the data are also significant because they are from tests of a subcutaneously administered formulation of the antibody cocktail, also referred to as REGEN-COV. An injectable version would make the treatment more accessible to a wider swath of the population compared to the currently authorized intravenous formulation, which must be given in infusion centers.

The drug from Tarrytown, New York-based Regeneron is a combination of two antibodies, casirivimab and imdevimab, both of which are designed to bind to the receptor-binding domain of SARS-CoV-2 to prevent the virus from infecting cells. Last November, the FDA granted emergency use authorization for an infused formulation of the cocktail as a treatment for mild-to-moderate Covid-19 in adults, as well as children 12 and older who weigh more than 88 pounds. That infusion is given over the course of 20 minutes.

Roche had signed on as a partner to help with manufacturing in order to increase global supply of the drug. The Swiss pharmaceutical giant is also taking the lead on clinical tests and regulatory submissions outside of the U.S.

The clinical trial results reported Monday were from a double-blind study that enrolled 1,505 uninfected people who lived in the same household as someone who had tested positive for the novel coronavirus within the prior four days. The study participants were randomly assigned to receive either the Regeneron cocktail as a subcutaneous injection, or a placebo.

According to Regeneron, 41% of the participants were Latino and 9% were Black. The company said that 31% of all study participants had at least one risk factor putting them at high risk of progressing to severe Covid-19 that may require hospitalization. Those risk factors include obesity, chronic kidney disease, diabetes, and a weakened immune system.

The results suggest that the Regeneron drug began working quickly. After the first week, the reduction in the risk of infection was 72%; in subsequent weeks that risk reduction increased to 93%. The 81% risk reduction measure was taken at day 29 of the study.

Myron Cohen, the director of the Institute for Global Health & Infectious Diseases at the University of North Carolina at Chapel Hill and the leader of the monoclonal antibody efforts for the NIH-sponsored COVID Prevention Network, said the clinical trial results suggest that the Regeneron drug can complement vaccination, particularly for those who are at high risk of infection.

“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,” Cohen said in a prepared statement. “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.”

Side effects if the antibody drug included injection site reactions. No study participants from either the treatment group or the placebo group withdrew from the study due to adverse events, and of the four deaths in the study (two in the test group, two in the placebo arm) none were attributed to Covid-19 or the study drug.

Antibody therapy is sometimes referred to as “instant immunity.” Unlike vaccines, which prompt the body to produce the neutralizing antibodies that confer immunity, antibody therapy readily provides those antibodies without the body needing to go through the process of making them. Such therapies are seen as offering an additional option for those who are immunocompromised or don’t respond well to vaccines.

Other Covid-19 antibody drug developers include Eli Lilly and Vir Biotechnology, which is working in collaboration with GlaxoSmithKline. Regeneron developed its antibody drug with funds from the Biomedical Advanced Research and Development Authority (BARDA).

Photo: Sezeryadigar, Getty Images



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