The Volokh Conspiracy

Mostly law professors | Sometimes contrarian | Often libertarian | Always independent

Volokh Conspiracy

The Moral Case for Testing Coronavirus Vaccines through "Challenge Trials" on Paid Healthy Volunteers

Doing so can potentially save many thousands of lives. And moral objections to this practice are weak. The issues here are very similar to the longstanding debate over whether we should legalize organ markets.


By now almost everyone recognizes how vital it is to develop an effective coronavirus vaccine as quickly as possible. A vaccine would save many thousands of lives that are otherwise likely to be lost to the virus. In addition, developing a vaccine may well be the only way to overcome the worldwide economic crisis caused by the disease. Even if lockdown orders are lifted, many people will still be unwilling or unable to return to anything like "business as usual" for so long as the coronavirus remains a threat.

The costs here are not just narrowly "economic." They also involve such things as foregone medical treatment leading to increased death from non-covid causes, growing hunger and poverty (especially in developing nations), and a reduction in childhood vaccinations that could imperil millions around the world. Anything that can make a vaccine available even a month or two earlier than would otherwise be the case could save a great many lives and avert much suffering.

But, in order to swiftly develop a vaccine, it may well be necessary to resort to "challenge trials": deliberately infecting healthy volunteer test subjects with the virus in order to then determine whether candidate vaccines work on them. My George Mason University colleague, economist Alex Tabarrok explains the reasons why here:

What if we develop a vaccine for COVID-19 but can't find enough patients to run a randomized clinical trial? It sounds absurd, but this problem has happened in the past. Ebola was identified in 1976, and candidate vaccines were proven safe and effective in mice and primates in 2004 and 2005, respectively. But no human vaccine was produced because it was extremely difficult, bordering on impossible, to trial an Ebola vaccine. The problem? Ebola is so deadly that people take precautionary measures long before a vaccine can be tested…

Vaccines are intended to prevent disease in healthy people, so they're tested for efficacy in healthy populations. But to test a vaccine, you need a population of still-healthy people who might get sick…

When a COVID-19 vaccine is available, it will be necessary to find a large population of people who are still at high risk of contracting COVID-19. This may be difficult. In developing countries, which may not be able to contain the virus, herd immunity may have developed. In richer countries, social distancing, testing and other measures may have made the probability of infection relatively low….

Even health care workers, however, have a low enough infection rate that you either need many months to determine if there is a significant effect, or you need large populations….

There is a second, related problem. Historically, most vaccine candidates fail. Thus, in a year or two, we want many vaccine candidates, not just one. But even if we are fortunate and have, say, seven vaccine candidates available, it probably won't be possible to run efficacy trials on all seven candidates….

The efficacy-trial bottleneck motivates the use of challenge trials. In a challenge trial, healthy individuals are split into two groups, one half vaccinated, the other not, and then both groups are infected or "challenged" with the virus. No waiting for natural infections here…

The virtue of a challenge trial is that the results would be available very quickly, within a few weeks, and using only a small population. If the vaccine is 50 percent effective, for example, then we would need around 100 volunteers or perhaps even fewer depending on how many people exposed to the virus in laboratory conditions contract the disease.

As Alex points out, these problems may foil early production and deployment of a promising vaccine candidate currently under development by scientists at Oxford University.  Challenge trials can fix this issue.

In this Washington Post article, philosophers Richard Yetter Chappell and Peter Singer make a strong utilitarian consequentialist case for challenge trials: the risk to the volunteers is greatly outweighed by the enormous benefits to others. There aren't many issues where Tabarrok—a libertarian—agrees with Singer (who is far more left-wing)!

Chappell and Singer are right in so far as they go. Any plausible cost-benefit analysis comes out the same way. But non-utilitarians might still have reservations, such as fears that paying volunteers to participate in challenge trials might lead to exploitation of the poor, "commodification" of the body, or the use of test subjects who are ignorant of the risks.

The challenge trial debate, gives me a strong sense of deja vu. For many years, I and others have argued that the government should legalize the sale of organs, so that thousands of lives can be saved—and much other suffering prevented—by increasing the number of organs available to those who need transplants. The arguments in that debate are very similar to those that can be raised against coronavirus vaccine challenge trials.

Thus, answers to standard objections to organ markets can also help justify coronavirus challenge trials. Consider, for example, the claim that paid challenge trials will exploit the poor. I answered that objection in the organ market context here:

[M]any people oppose legalizing organ markets because they believe it would lead to exploitation of the poor. But most of them have no objection to letting poor people perform much more dangerous work, such as becoming lumberjacks or NFL players. If it is wrong to allow poor people to assume the risk of selling a kidney for money, surely it is even more wrong to allow them to take much greater risks in order to increase their income.

If you believe that organ markets must be banned because they exploit the poor, you must also argue that the poor should be forbidden to take jobs as lumberjacks and football players. If you believe that such considerations justify banning participation in organ markets even by the non-poor, than we must also categorically forbid monetary compensation for football players. Indeed, the case for banning the payment of football players is actually much stronger than that for banning organ markets. Unlike the ban on organ markets, a ban on professional football would not lead to the deaths of thousands of innocent people.

If you still worry that the poor will be "exploited" in either organ markets or challenge trials, I offer the second-best solution of restricting participation in such markets and  trials to the nonpoor. Simply adopt a rule that all test subjects must have incomes above whatever threshold you think is enough to avoid "exploitation" (e.g.—above the poverty line or above the average income in the participant's country).

We do not need an infinite supply of volunteers for challenge trials. Just a few thousand. It should be possible to find them even if participation is limited to those above a certain income floor. As of this writing, the admirable "1 Day Sooner" website has already gathered over 25,000 volunteers who are willing to participate. Many, perhaps most of them, are not poor. And surely we can find more such volunteers, if need be.

Here is my response to claims that paying organ donors (and by extension Covid challenge trial participants) will somehow unjustly "commodify" the body:

Other critics believe that organ markets must be banned because it is inherently wrong to "commodify" the human body. Yet most of them have no objection to letting a wide range of people profit from organ transplants, including doctors, insurance companies, hospital administrators, medical equipment suppliers, and so on. All of these people get paid (often handsomely) for helping transfer organs from one body to another.

Perversely, the only participant in the process forbidden to profit from the "commodification" of organs is the one who provided the organ in the first place. If you believe that people should be forbidden to sell kidneys because earning a profit from organs is immoral "commodification" of the body, you must either oppose paying all the other people who currently earn money from organ transplants, or explain why they, unlike the original owner of the kidney, are not also engaged in commodification…..

What is true of organs is also true of vaccines. Scientists, drug manufacturers, doctors and others stand to profit from the development of a Covid vaccine, which necessarily involves human trials of one type or another. Challenge trial participants should be allowed to do so, as well.

I would add that we pay volunteers to risk harm to their bodies in many other contexts. Soldiers, police, firefighters, lumberjacks, coal miners, and professional football players are all examples. Participants in many of these professions accept greater risks than organ donors or young, healthy Covid-19 challenge trial participants are likely to undergo. If "commodification" is fine for lumberjacks, police, and firefighters, it should be permissible for challenge trial participants, as well.

There is, of course, a danger that some participants will not be properly informed of the risk. But that can be minimized by securing "informed consent" ahead of time, as is already required for medical procedures.

The information available to participants may well be imperfect. Covid-19 only appeared a few months ago, and there are still uncertainties about its effects. But we allow people to voluntarily take imperfectly understood risks for pay in many other contexts. For example, soldiers and police often do not know ahead of time exactly what sorts of dangers they may face in the course of doing their jobs. It is notoriously difficult to predict what risks may arise in future battles. The moral requirement of informed consent can surely be satisfied if volunteers are given the best information available at the time, and also informed that there are some risks involved that experts may not yet fully understand.

It is also worth noting that there are already volunteers available who do have a solid understanding of the risk, and who are not readily dismissed as desperate poor people ripe for "exploitation." Consider, for example, this article by Princeton student Isaac Martinez, explaining his willingness to volunteer, or this one by Bloomberg columnist Faye Flam, discussing her decision to do so.

There may be some who object to challenge trials even if the participants are not paid, on the ground that it is intrinsically immoral to deliberately subject healthy people to the risk of a deadly disease, even if they consent. But, as already discussed, we routinely allow volunteers to take risks with their lives and health in a variety of other contexts, including many where the potential benefits are far smaller than here. If it is not immoral to allow soldiers, police, and firefighters to take such risks, the same goes for challenge trial participants.

Like others who risk their lives to benefit others, challenge trial volunteers deserve our gratitude, and proper compensation for their efforts. And there is no good moral justification for forbidding them to take those risks. To the contrary, we should move ahead with challenge trials as soon as feasible. Every day of delay could literally be a matter of life and death—a great many lives and deaths.