Key criteria for the ethical acceptability of controlled human infection studies during public health emergencies

Controlled human infection studies (CHIS) involve the intentional infection of volunteers with pathogens, including those that cause epidemics or pandemics. These studies can be highly valuable for responding to public health emergencies, although they often raise ethical and scientific challenges. For example, CHIS conducted during the COVID‑19 pandemic provided data on coronavirus infection and the accuracy of diagnostic methods. It is reasonable to expect that this type of study will be proposed in future emergencies, making it urgent to clarify now the criteria needed to ensure that CHIS are conducted in accordance with the highest ethical standards. This  WHO document provides guidance to scientists, research ethics committees, national authorities responsible for ethical oversight of research, funders, national regulatory authorities, and policymakers on the core criteria that should be considered when assessing the ethical acceptability of these studies.