Young, healthy people will be intentionally exposed to the virus responsible for COVID-19 in a first-of-its kind ‘human challenge trial’, the UK government and a company that runs such studies announced on 20 October. The experiment, set to begin in January in a London hospital if it receives final regulatory and ethical approval, aims to accelerate the development of vaccines that could end the pandemic.

Human challenge trials have a history of providing insight into diseases such as malaria and influenza. The UK trial will try to identify a suitable dose of the virus SARS-CoV-2 that could be used in future vaccine trials. But the prospect of deliberately infecting people — even those at low risk of severe disease — with SARS-CoV-2, a deadly pathogen that has few proven treatments, is uncharted medical and bioethical territory.

Proponents of COVID-19 challenge trials have argued that they can be run safely and ethically, and that their potential to quickly identify effective vaccines outweighs the low risks to participants. But others have raised questions about the safety and value of these studies, pointing out that large-scale efficacy trials involving tens of thousands of people are expected to deliver results on several COVID-19 vaccines soon.

“Deliberately infecting volunteers with a known human pathogen is never undertaken lightly. However, such studies are enormously informative about a disease,” said Peter Openshaw, an immunologist at Imperial College London and investigator on the study, in a press statement. “It is really vital that we move as fast as possible towards getting effective vaccines and other treatments for COVID-19, and challenge studies have the potential to accelerate and de-risk the development of novel drugs and vaccines.”