plasma

In the 1970s, a new treatment using donated human blood plasma was developed to replace these clotting agents.

This was much harder to administer, but was made from the blood plasma of a single donor, lowering the infection risk.

Sam's father Gary was one of more than 1,200 people infected with HIV as part of the infected blood scandal, most after being given a drug made from US blood plasma in the late 1970s and 1980s.

In the early 1980s, the UK could not keep up with demand for Factor VIII, which was made by pooling - or mixing - the blood plasma of thousands of individual donors.

In the UK, blood donations have always been voluntary, but in the US, drug companies were allowed to pay cash for plasma.