Any guess on the mechanics?
Yes. Unlike whole blood transfusions, which are handled one unit at a time, blood plasma goes into a vat with thousands of units. One diseased donor can contaminate the whole lot -- thousands of units. Then the vaccines, gamma globulin and Factor 8 made from the plasma are contaminated. That was the mechanism for the spread of AIDS and Hepatitis C from the tainted plasma from Cummins Prison Farm in Arkansas under Bill Clinton -- the Blood Trail story we've traced in this forum since 1998. We've followed that bad blood all over the world, including Africa. Everywhere it went, it caused Hepatitis and AIDS.
Peter Duesberg is full of it when he says that AIDS is not spread by a blood-borne virus.