All this attention to challenge trials of the novel coronavirus might give the impression that they’re ready to launch. They aren’t, and not just because of ethical concerns. Researchers need to produce challenge strains, identify suitable trial sites, prepare secure research facilities and develop ethical protocols — and should begin that work now. Researchers and funders should discuss barriers, concerns and solutions with the public, regulators and public health officials who will lead vaccine rollout.

These preparations are not themselves a green light. But they will enable a clearer picture of the risk and value of coronavirus challenge studies once they are ready to begin, to inform decisions about whether and how to deploy them. An independent expert panel should then be engaged to make those decisions, ruling out excessively risky or insufficiently valuable trials, insulated from potential biases from having invested in preparation and public pressure to proceed.

We have to know that volunteers were not exposed to risk in vain. Public trust in vaccines and research depend on it.