Regeneron has released positive initial results from an ongoing phase 1/2/3 study evaluating its antibody cocktail of casirivimab and imdevimab in hospitalized COVID-19 patients who require low-flow oxygen.

The trial is assessing patients who had not started mounting an immune response to the coronavirus, measured by the lack of antibodies in their system, referred to as being seronegative. The seronegative patients receiving the cocktail had a reduced risk of mortality risk and of needing mechanical ventilation of approximately 50 percent, the company said.

In total, the trial enrolled 217 seronegative and 270 seropositive patients, with both groups receiving low-flow oxygen.

Regeneron’s CEO George D. Yancopoulos cautioned that “while the virology results from this analysis of hospitalized patients were robust, the clinical efficacy data are based on a small data set of events and cannot be viewed as conclusive at this stage.”