[raphaelj]

Isn't it exactly what happened? Some vaccines started large scale tests around March/April.

It's just that you have to wait a few months to know if the vaccine you're testing is effective. You can't make this delay shorter with more volunteers.

And when you're fighting a decease that "only" kills 0.5% of the people inflected, your risk margin is pretty low (what if your vaccine creates deadly consequences to 0.6% of the people vaccinated?).

[maxerickson]

Challenge trials shorten the period by intentionally exposing the volunteers to the infection.

The mRNA vaccines had to wait until November to get enough infections.

There can be an issue that the measurement of the effectiveness of the vaccine is then related to the exposure protocol (which may not be the same as typical natural infections), but it's reasonable to expect results much sooner.

[andreareina]

So, you'd have to tell the participants that they're going to be deliberately exposed to the virus; I don't think you're going to get a representative sample of the population agreeing to that.

[sterlind]

People volunteer for military service even during wars, but you're right. Challenge trials won't be brimming with 75-year olds, the same way 75-year olds don't enlist. You'd learn that the vaccine works on healthy 20-somethings though, and that might have been enough for approval.

[andreareina]

Should it be?

[snovv_crash]

If you can prevent 20 and 30 year olds from being infected, you might just manage to halt the spread of the virus even if you don't confer individual immunity onto older people.

[maxerickson]

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).

[BurningFrog]

You can recruit the demographics you need by paying them enough.

Challenge trials need far fewer people, so paying each one $1M is feasible.