The novel coronavirus is inflicting global suffering that is likely to persist until scientists produce an effective vaccine. With so much hinging on a vaccine, some are calling for a little-known epidemiological tool to speed testing: human challenge trials. Under certain conditions, human challenge trials — in which individuals volunteer to be deliberately exposed to a pathogen — could hasten vaccine development by giving scientists rapid feedback about what is and is not working. Given the pandemic’s mounting destruction, proposals that could set the world on a path to recovery sooner — even risky proposals — should be considered.

Conventionally, after a vaccine is shown to be safe in humans, thousands of volunteers are divided into two groups: Half get the vaccine, half get a placebo. As volunteers go about their lives for months, some fraction of both groups will be exposed to the pathogen. Researchers compare groups to see whether fewer of those who were vaccinated got sick. With challenge trials, instead of waiting for months and hoping enough participants are exposed — which could be tricky under social distancing orders — young, healthy people agree to be exposed to the pathogen and then are observed, providing much faster evidence of a vaccine’s effectiveness. Because challenge trials guarantee exposure to the pathogen, they also could provide useful information with many fewer participants.

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