On Jan. 26, 2021, Regeneron announced positive initial results from an ongoing Phase 3 clinical trial evaluating REGEN-COV (casirivimab and imdevimab antibody cocktail) used as a passive vaccine for the prevention of COVID-19 in people at high risk of infection (due to household exposure to a COVID-19 patient). The trial was being run jointly with the National Institute of Allergy and Infectious Diseases.