Immunity detected in blood from 2015 - was the virus already there then?

- It may well have circulated locally in the Wuhan area before the pandemic broke out and gradually adapted to humans.

It is very difficult to say how long, but why not months to a year, says Björn Olsen, professor of infectious disease medicine.

At the same time, t-cell immunity to the coronavirus has been detected in donated blood in the United States as early as 2015-2018.

In the clip, Björn Olsen and immunologist Gustaf Christoffersson explain how it goes together.