“There’s this emerging consensus among everyone who has thought about this seriously,” said Prof Nir Eyal, the director of Rutgers University’s Center for Population-Level Bioethics in the US.

The prospect of infecting healthy individuals with a potentially deadly pathogen may sound counterintuitive, but according to Eyal the risk of death from Covid-19 for someone in their 20s is around one in 3,000 – similar to the risk for live kidney donation. In this case, the potential benefits would extend not to a single individual, but to thousands or millions who could be protected by a vaccine.

“Once you give it thought, it is surprisingly easier to approve than dispatching volunteers as part-time medical workers and other practices that we’ve already accepted,” he said.