Continuing the discussion from 1DaySooner: Open Letter on Challenge Trials for COVID-19:
I’ve raised these objections too.
That’s one point that has to be made up front. Now we have to ask what challenge trials would be for in our situation. The idea is that they would speed up vaccine development, giving us more data more quickly in Phase II trials (which is where we really start testing to see if any given vaccine candidate can be protective). But I don’t think we need to run challenge trials at all – not under current conditions. We have areas where the coronavirus is spreading so well through the population that I don’t see the advantage.
In the end, despite the heroic sound of the idea, I think that such trials are (1) still ethically questionable, (2) fraught with legal complications, (3) are for those reasons and others not likely to run meaningfully faster than regular Phase II trials, and (4) will produce data that may not be able to be extrapolated to the real-world situation. I don’t see the point.
That last point is particularly important:
Now consider who those volunteers would be – who they would have to be. Young, healthy people – who else? We’re already stepping close to the line with the whole idea, and giving it to anyone in a more at-risk population would surely step over it. But even the Phase I safety trials of the vaccines have brought in age groups that would be unacceptable in a challenge trial for Phase II, and the Phase II trials – since they’re taking place out “in the wild” can similarly enroll people who would never be in a deliberate challenge. This means that the data you would obtain from such a challenge is skewed heavily away from some of the people that you are going to want to treat first. Both efficacy and safety can (and do) vary by age, existing medical conditions and other variables that you’re going to have to make sure to not address in the challenge trial.