Many high-income countries have rapidly pivoted from hard decisions about who may receive COVID-19 vaccines, due to shortages, to equally hard decisions about who must receive them. As lasting containment of COVID-19 remains elusive, many nations—from Costa Rica, to Austria, to Turkmenistan—are turning to vaccination mandates of various kinds.

Mandates, however, are controversial in many countries. Austria's proposed mandate for adults, for example, provoked mass protests. Some objectors argue mandates represent undue encroachment on individual liberty. Some other objectors maintain that mandates will not be an effective policy for COVID-19 because many individuals will seek to evade them, and mandates might erode support for other public health measures such as mask wearing.

In this Viewpoint we consider the likely effectiveness of policies that require COVID-19 vaccines in improving vaccine uptake and reducing disease in the USA, in view of the evidence from past vaccination mandates and distinctive aspects of COVID-19. Two dimensions of effectiveness in improving uptake are relevant: (1) target-group effectiveness (the extent to which a mandate improves uptake of vaccines in the group covered by the policy) and (2) population effectiveness (the extent to which mandate policies improve vaccination coverage in the US population).