3 ms·

You need a lot of participants because the expected outcome is that you inject a novel foreign substance into billions of people. At some point, you have to tes

by runako 6y ago

You need a lot of participants because the expected outcome is that you inject a novel foreign substance into billions of people. At some point, you have to test for safety too, and very small trials are not good for that. And again -- the backup therapeutics that enable any challenge trial were not broadly available until a month or two before vaccines went into wide deployment. (You will note that nobody is volunteering for a challenge trial for any drugs or vaccines for our other ongoing pandemic, HIV. Lack of backup therapeutics is a big reason for that.)

Closi 6y ago
You still need to test for safety, that's definitely true. At least you know you have a viable candidate though I guess. People were actually volunteering for a challenge trial for Covid prior to theraputics being available - because Covid actually is low-risk for the groups in the challenge trial (young people) and the vast majority of people recover. I don't think theraputics are necessary for a challenge trial, as long as there is sufficient benefit, the risk is sufficiently low, and volunteers are aware of the personal risks (aware this criteria is ambiguous!). HIV is incurable, however there are excellent therapeutics. Despite this, the prognosis of HIV is much worse than someone with Covid.