> The main benefit of challenge trials is to speed up development as I understand it not to broaden risk estimates.
Right, which is why it was crucial to have such trials a year ago. We could have shipped vaccines 3 months sooner and saved hundreds of thousands of lives.
Unfortunately, no health authority was willing to risk blame for any disabilities or deaths stemming from deliberately exposing consenting people to covid. So we had to use much larger sample sizes and wait longer to know which vaccine candidates were effective.