[s1artibartfast]

>An issue with doing a COVID-19 challenge trial that I heard from someone in this space at the time: Nobody actually knew how much virus to administer. We weren't sure of the normal quantity of COVID-19 a person typically inhales before becoming sick.

I dont think that is accurate. You dont have to know the actual viral quantity transmitted to create a representative transmission event. That is to say, if you know people can catch covid sitting side by side, that can be your challenge.

Even if the scenario isn't perfect, you still know how many people caught it vs placebo.

[Wowfunhappy]

Yes, but again: If you gave participants an ineffective or placebo vaccine followed by 10+ times the normal dose of COVID, how many of them would die?

If you're okay with potentially killing most of the trial participants, I suppose you could still get useful data, but the ethics become significantly more questionable IMO.

Edit: I just re-read your post. I think you're saying, you wouldn't actually give anyone the COVID virus directly, you'd just find someone who was known to have contracted COVID in the wild and bring them in to purposefully expose trial participants. That is an interesting idea which I've never seen discussed in the context of a challenge trial. I'd be interested to read more about why this is not typically done.

[s1artibartfast]

Getting a 10x Lethal dose just doesn't seem like a realistic concern to me, and certainly not a dealbreaker.

We know and knew what a normal exposure was: being in close proximity to one or more contagious people for somewhere between a few minutes and many days.

If you have someone sit next to an infected person for an hour, how do you get to this hypothetical 10x super dose?

Edit: I would also add that medical trials also have well established methods of determining effective and dangerous exposure levels, and these are used in almost every Phase 1 trail. You start with extremely low exposure, then increase it until you see dangerous outcomes. This could easily be done with a covid serum to find the infectious but non-lethal level. for example, if you think X amount of covid virus is infectious, you start at 0.0001 X and then increment up, to find the amount that causes normal infection, and not some lethal mega dose.

[Wowfunhappy]

> Edit: I would also add that medical trials also have well established methods of determining effective and dangerous exposure levels, and these are used in almost every Phase 1 trail.

Yeah, so the scientist I heard this from didn't say it would be impossible to find the right dose, just that we didn't know the dose yet and we'd have to find it before running a challenge trial.

He thought this erased the time savings of a challenge trial versus the normal process.