Should we have “challenge studies” where participants are deliberately infected with Covid to test vaccines?

See Shouldn't the public decide? by Scott Sumner.

"Right now, about 7.8 billion people are intensely interested in the question of when the coronavirus problem will abate. Even those living in poor tropical countries with low rates of infection and a very young population, say Nigeria, are impacted by the huge drop in commodity prices.

While there is a great deal of promising research on vaccines, the process takes a long time. But what if there were a way to speed up the process of vaccine development through deregulation? In fact, there is such an option, although it is controversial.

When vaccines are tested, it is difficult to get statistically significant results if the infection rates are low. Thus a random group of 1000 volunteers might end up not being exposed to the virus, especially in this era of social distancing. For this reason, medical scientists often rely on “challenge studies” where participants are deliberately infected with a virus.

You can probably already see the problem—is it ethical to deliberately infect people with a dangerous virus?

On the other hand, this idea is not as wacky as it might seem:

1.  We do challenge studies with flu vaccines.  Yes, the coronavirus is more dangerous than the flu.  But these studies would be done with young adults, for whom the risk is only modestly higher than for the flu, not dramatically higher as with a 70-year old.  (I mean only slightly higher in absolute terms; I’m not sure how much higher the risk is in relative terms.  But with ethical questions, it’s absolute distinctions that matter.)
2.  A recent article in Nature suggests that challenge studies of Covid-19 vaccines might well be ethical, and indeed might even be beneficial for the participants themselves.
3.  There are vaccines that might be available as soon as September, but also might be held back for a long period due to the inability to do challenge studies.  Given how severely this pandemic is damaging the world (in terms of health, wealth and happiness), this potential roadblock is a really big deal.

I’d favor paying volunteers, but given what’s at stake it might be possible to find 1000 people to volunteer without pay.  Lots of young people volunteer to fight in wars.  We could give each of them a Presidential Medal after it’s over.

Some fear that providing financial incentives would “prey on the poor”:

I happen to be a bioethicist who doesn’t have huge objections to attracting study participants by offering financial incentives. But I think in this study, ensuring a high level of public trust is important, and I would advise researchers not to attract volunteers through high payments. This would have the advantage of making sure that the study doesn’t prey on the poor.

If that’s really such a problem then you could have income quotas, where the percentage of poor and non-poor participants is roughly in line with the US population.  I actually think that sort of quota would be “preying on the poor”, not helping them; I’m just saying that none of the traditional objections actually hold water.  If we really want to do this, we can find an ethical way of doing so.
The Nature article advocating a challenge study suggests the participants would be divided into two groups, one of which gets a placebo.  But while I understand that’s standard procedure, I wonder if it is necessary in this case.  Someone correct me if the following is wrong:

Don’t we already know from numerous natural experiments that a very large proportion of people exposed to the virus will become infected?  And that’s in natural conditions such as passengers on the Diamond Princess or workers in a Korean call center.  If the virus challenge were more direct and intentional, wouldn’t the infection rate be extremely high, so that the vaccine could be tested without a (unprotected) control group?

This is a highly contagious disease, indeed one that some scientists believe 50% of people are likely to contract at some point.  Under those conditions, how dangerous is a challenge study giving a vaccine that has already provided strong hints of effectiveness (in previous studies) to a bunch of healthy young people?

Right now, these decisions involving the well being of the entire world are not being made by you or me or Xi Jinping or President Trump or the US Congress.  They are not being made by free individuals making free choices. Rather, they are being made by a few medical ethicists.  My hunch is that the public as a whole is more “utilitarian” than the average medical ethicist.  Should a decision this important be made by the public?  Shouldn’t they at least be consulted.

Notice how the media slides over this issue.  Here’s a story from Business Insider:

“We may get enough data in a couple of months to see if the vaccine works, but if transmission levels drop, this could take up to six months,” the group said on Thursday.

No mention of the fact that medical ethicists might put the planet through 4 additional months of misery by banning challenge studies, and the public doesn’t even know that.

Of course I might be wrong, and I look forward to clarification in the comment section.  I have an open mind.  I request, however, that you read the Nature article, and don’t just assume I’m an economist who “just doesn’t understand these issues”.  Nature is a prestigious outlet, which doesn’t typically publish papers written by crackpots.

It’s also possible that the roadblock is not medical ethics, but some other problem such as our dysfunctional tort law system.  However, I was already skeptical of medical ethicists, due to their frequent support for laws banning kidney markets.  These laws kill tens of thousands of Americans each year."