3 ms·

None of them intentionally give the live virus to their subjects.

• viraptor 6y ago
  That would speed up the test, sure. But as far as the quality of the results goes, why is that different from the existing test where a large number of vaccinated (real and placebo) subjects gets exposed/infected? It's still testing efficacy.
• Kliment 6y ago
  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.