Challenge studies get performed on non-human (animal) test subjects (this was done for the Biontech/Pfizer vaccine), and there's a volunteer human challenge study planned in the UK for January. A challenge study is one where you intentionally give a live virus to your subjects.

Arguably, releasing your subjects into an environment full of live virus, such as the United States, is a kind of challenge study, which rapidly delivers efficacy data. This is why approval could happen so much faster than usual for these vaccines.