• decision-making
• health care economics
• social control of human experimentation

We largely agree with Grimwade et al’s1 conclusion that challenge trial participants may ethically be paid, including for risk. Here, we add further arguments, clarify some points from the perspective of economics and indicate areas where (behavioural) economists can support the development of a framework for ethically justifiable payment. Our arguments apply to carefully constructed and monitored controlled human infection model (CHIM) trials that have been appropriately reviewed and approved.

Participants in medical studies perform a service. Outside the domain of research participation, there is nearly universal agreement that workers providing a service should be compensated fairly, and that work involving more discomfort and risk should be compensated more generously. Accordingly, labour regulations impose floors (minimum wage laws), not caps on compensation. Caps, even if intended to protect against undue inducement, also raise concerns about illegal price-fixing that disadvantages workers. Such limits on payment for egg donors have successfully been challenged in court.i

Moreover, caps on compensation may harm everyone at risk of infection, not just potential participants. Insufficient compensation may impede the recruitment of enough suitable subjects, for example, when representativeness of the subject sample is required. Delays in vaccine development not only prolong disruption of social, educational and economic activity but also lead to excess infections and deaths. Unlike paid CHIM participants, individuals exposed to such infection do not accept it voluntarily, are not compensated for it, and are unlikely to receive the level of medical supervision afforded to closely monitored CHIM participants.

Payment caps can lead to attempts to circumvent the regulation. For example, many countries …