Regeneron's COVID-19 antibody cocktail cuts risk of death by 20% in seronegative patients

Study results announced Wednesday showed that the addition of Regeneron Pharmaceuticals' antibody cocktail REGEN-COV to usual care reduced the risk of death by 20% in patients hospitalised with severe COVID-19 who had not mounted a natural antibody response on their own against SARS-CoV-2, compared to usual care alone. The therapy, which combines the monoclonal antibodies casirivimab and imdevimab, is currently authorised for the treatment of mild-to-moderate COVID-19 in those who are at high risk for progression to severe disease.

"People have been very, very sceptical, that any treatment against this particular virus would work by the time people get in hospital," remarked Martin Landray joint chief investigator for the RECOVERY trial. "We now know that this antibody combination is not only bad for the virus but it is also good for the sickest patients who have failed to mount a natural immune response of their own," Landray said, adding "it is the first time that any antiviral treatment has been shown to save lives in hospitalised COVID-19 patients."

Benefit only in seronegative patients

The RECOVERY study evaluated REGEN-COV after an earlier Phase I/II trial in hospitalised patients pointed to a benefit in those who were seronegative, including a reduction in the risk of death. The RECOVERY study randomised 9785 patients hospitalised with COVID-19 to receive usual care plus REGEN-COV by intravenous infusion or usual care alone, with about one-third of the participants seronegative at baseline.

Results showed that for the primary outcome, 24% of seronegative patients in the REGEN-COV group died versus 30% in the usual care group by day 28. Regeneron added that when combining the larger seropositive group with the seronegative patients, there was no longer a significant effect on 28-day mortality, with mortality rates of 20% in the REGEN-COV group compared to 21% in the usual care group. Meanwhile, among patients who received usual care alone, 28-day mortality was 30% in those who were seronegative compared to 15% in those who were seropositive at study entry.

Hospital duration also cut

Further results showed that for seronegative patients, the duration of hospital stay was four days shorter among those who received REGEN-COV versus the usual care group, while the proportion of patients discharged alive by day 28 was 64% and 58%, respectively. In addition, among the seronegative patients not on invasive mechanical ventilation at baseline, the risk of progressing to the composite endpoint of invasive mechanical ventilation or death was 30% for those given Regeneron's therapy, compared to 37% for usual care.

"The trial was conducted at a time when most patients had not been fully vaccinated," explained David Weinreich, Regeneron's executive vice president for global clinical development. "These results provide hope to patients who have a poor immune response to either the vaccine or natural infection, as well as those who are exposed to variants for whom their existing antibodies might be sub-optimal," Weinreich said.

Meanwhile, Regeneron's chief scientific officer George Yancopoulos said "we intend to rapidly discuss these results with regulatory authorities, including in the US where we will ask for our EUA to be expanded to include appropriate hospitalised patients." Earlier this year, the company reported results from another Phase III trial showing that REGEN-COV lowered the likelihood of at-risk COVID-19 patients progressing to hospitalisation or death, while a subsequent late-stage study found that the antibody cocktail reduced the risk and burden of COVID-19 among household contacts of SARS-CoV-2-infected individuals.

Regeneron is collaborating with Roche to increase the supply of REGEN-COV, with the Swiss drugmaker mainly responsible for development and distribution of the product outside the US.

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