Yeah, I dunno. I don't see why there couldn't be a challenge arm to a trial that also did a larger group with no challenges.
The challenge arm wouldn't have any influence over the other arm (and likely not much impact on recruitment), but might provide results for some groups much faster. Starting vaccinations on younger healthcare workers in August seems like it would have been a win (assuming they had data to justify it by that point).
The challenge arm wouldn't have any influence over the other arm (and likely not much impact on recruitment), but might provide results for some groups much faster. Starting vaccinations on younger healthcare workers in August seems like it would have been a win (assuming they had data to justify it by that point).