The tragedy of the clinical commons

I've been meaning to write about this topic for months, but was reminded of it only when scrolling through my open browser tabs. One of the tabs was this blog post by Derek Lowe from last October, when the first clinical trials of coronavirus vaccines were about to start reporting results:

We’re getting closer to having to deal with a number of tricky issues around the first Emergency Use Authorizations (EUAs) for coronavirus vaccines. These have never quite come up in this way before, because (for one thing) EUAs for vaccines are relatively rare events, and (for another) we’ve never had so many simultaneous vaccine trials against the same disease before.

So let’s just stipulate that Somebody (be it Pfizer, Moderna, AstraZeneca, whoever) asks for an EUA before all the other Somebodies, and that this request is granted...

We may get into a situation where an interim readout of the data show that a vaccine may well be working, but that granting an immediate EUA has a real danger of blowing the statistics for the complete trial. That is truly the worst outcome: ending up with something that might be useful, but being unable (despite all the time and money and effort) to able to say if it really is. We’ve got to avoid that...

But the patients involved in all these trials may have other ideas. Each individual that decides to leave the trial protocol may feel that loss of their own data is not enough to affect the overall result, but if enough people think that way, that result will most certainly suffer – a tragedy of the clinical commons...

In the same way that you can’t force the participants of the emergency-authorized vaccine trial to stay in it, you also can’t force the participants in the other trials not to get the newly authorized one 

The Tragedy of the Commons arises in the case of common resources - goods that are rival (one person's consumption reduces the amount of the good available for everyone else), and non-excludable (if the good is available to anyone, it is available to everyone, and you can't easily prevent people from having access to it). How does this apply to the case of vaccine clinical trials? Vaccine trial participants are rival (since one participant leaving the trial reduces the number of participants remaining in the trial), and non-excludable (for medical ethics reasons, you can't stop a trial participant from leaving the trial). As each trial participant leaves the trial, fewer participants remain in the clinical trial, and eventually so few participants would be left in the trial that the results of the trial become meaningless.

The Tragedy of the Commons happens because private incentives and social incentives differ. The private incentive for the trial participants is to get vaccinated, even if in order to do so it means leaving the clinical trial they are enrolled in. The social incentive is for trial participants to remain in their clinical trial until it is completed.

Fortunately, we didn't find ourselves in a situation where one vaccine was given Emergency Use Authorisation well in advance of the others. Clinical trial participants mostly followed through on their commitment to complete the trial, and we ended up with several coronavirus vaccines that were shown to be effective. Fortunately, the 'tragedy of the clinical commons' was avoided.

[HT: Marginal Revolution]