Spanish drugmaker Grifols has begun a late-stage trial to evaluate its anti-coronavirus hyperimmune globulin, which is derived from the plasma of recovered COVID-19 patients.

The phase 3 trial is being conducted in collaboration with the Biomedical Advanced Research Development Authority, the National Institute of Allergy and Infectious Diseases and the FDA.

The study’s goal is to find out whether treatment during initial symptoms could strengthen the antibody response and reduce the risk of serious illness or death. Patients will be given either a combination of the hyperimmune globulin and remdesivir or remdesivir and placebo.

The phase 3 trial will enroll 500 COVID-19 patients in up to 58 hospitals spanning 18 countries, including the U.S. and Spain.