In an exploratory analysis conducted on the first approximately 400 evaluable individuals enrolled in the phase III trial, the researchers found that passive vaccination with Regen-CoV resulted in 100% prevention of symptomatic COVID-19 infection and approximately 50% lower overall rates of infection than those who had received only placebo, Regeneron said. What's more, those who had received Regen-CoV and had asymptomatic infections experienced markedly decreased levels and duration of viral shedding.

Infections in the placebo group had an average of more than 100-fold higher peak load. Furthermore, infections in the Regen-CoV group lasted no more than one week, while about 40% of infections in the placebo group lasted three to four weeks, Regeneron said. None of the infected individuals in the Regen-CoV group had high viral loads, compared with 62% of the infected placebo group, according to the firm.

The trial is being run jointly by Regeneron with the U.S. National Institute of Allergy and Infectious Diseases (NIAID). The company said it expects to have confirmatory phase III results in the second quarter.