Abstract

At the height of the Covid pandemic, there was much discussion in the literature about using human challenge trials (HCTs) to expedite the development of effective Covid-19 vaccines. Historically, reluctance to fully accept HCTs has largely been due to potential conflicts with the principle of nonmaleficence in bioethics. Only a few commentators have explored this topic in depth. In this paper, we claim that to address ethical concerns regarding HCTs, two types of ethical reasons should be identified and investigated: first-order reasons that can be given to claim that a practice in itself is in direct conflict with the principles of bioethics; and second-order reasons that take into consideration how a practice is carried out and its consequences. We argue that understanding these ethical reasons is crucial for guiding the implementation of HCTs. We investigate a first-order reason against HCTs when the practice is in conflict with the principle of nonmaleficence, and when it is not. Following this argument and assuming there is no first-order reason based on nonmaleficence that hinders using HCTs, we argue there may be second-order reasons to guide implementation of this practice, such as difficulty in obtaining informed consent; protection of the weaker party; and trust in the scientific enterprise.