Two years into the coronavirus disease 2019 (COVID-19) pandemic and following several hot debates, the world's first COVID-19 human challenge trial has recently been published by Killingley et al. We review its findings and explain why this particular juncture in time makes additional challenge trials for COVID-19 and for other diseases justified and important.
Keywords: COVID-19; controlled human infection model; human challenge trials; research ethics; vaccine ethics.
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