Eyal et al have recently argued that researchers should consider conducting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) human challenge studies to hasten vaccine development. We have conducted (J. L.) and overseen (L. D.) human challenge studies and agree that they can be useful in developing anti-infective agents. We also agree that adults can autonomously choose to undergo risks with no prospect of direct benefit to themselves. However, we disagree that SARS-CoV-2 challenge studies are ethically appropriate at this time, for (...) 3 reasons: (1) current scientific knowledge of SARS-CoV-2 infection is insufficient to manage risks; (2) autonomous decision making, while necessary, does not override concerns about risk; and (3) undertaking challenge studies now would imperil confidence in the research enterprise, potentially undermining the global response to the coronavirus disease 2019 (COVID-19) pandemic. (shrink)