Shares of the Tarrytown, N.Y., company at last check were up 3.7% to $645.14.
The trial, run jointly with the National Institute of Allergy and Infectious Diseases, would test the cocktail's ability to prevent infection in 2,000 people who have been exposed to the virus by close contact, such as by housemates.
The company said that a separate Phase II/III trial is testing the antibody cocktail therapy as a treatment in 2,900 coronavirus patients who are in hospitals and ambulatory settings. That trial is being run in the U.S. and in other countries like Brazil and Mexico.
"We are running simultaneous adaptive trials in order to move as quickly as possible to provide a potential solution to prevent and treat covid-19 infections," George Yancopoulos, co-founder, president and chief scientific officer, said in a statement.
Last week, Regeneron and Sanofi (SNY) - Get Report said a group of covid-19 patients requiring mechanical ventilation failed to show measurable improvement when treated in a Phase III trial with the rheumatoid arthritis treatment Kevzara.
Last month, Regeneron said it began human testing of its experimental antibody cocktail to treat the coronavirus.
The company said that the program will consist of four study groups: hospitalized covid-19 patients; non-hospitalized symptomatic covid-19 patients; uninfected people in groups that are at high-risk of exposure, such as healthcare workers or first responders; and uninfected people with close exposure to covid-19 patients.
Anthony Fauci, the immunologist who directs the NIAID and is a member of the White House Coronavirus Task Force, said in an interview last month with TheStreet.com that he "was cautiously optimistic that the development of monoclonal antibodies by Regeneron, by [Eli] Lilly, (LLY) - Get Report by a variety of other companies, would actually get us closer to a good and effective therapy."