In order to provide the F.D.A. with the kind of data it would need to approve a change in dosing, scientists must first study blood samples from patients who participated in the Phase III trial to determine precisely what immune response correlates with protection against Covid-19.
Then, Dr. Mascola said, researchers would have to either look back at patients from the Phase II trial, or conduct a new one, to demonstrate that patients who received the 50 milligram dose developed the threshold immune response. If the results looked promising, he said, “all this then needs to be put together as a data package for review and discussion with F.D.A.”