This article proposes a novel defense of vaccine mandates: such policies are justifiable because they protect the capabilities of individuals who cannot cultivate individual immunity against infection. We begin by considering a nearby argument that has recently enjoyed popularity, which claims individuals have an enforceable obligation to get vaccinated because they have benefited from community protection (often referred to as ‘herd immunity’), and thus they ought to do their fair share in sustaining that public good by getting vaccinated. We object, (...) however, that this kind of argument misstates the ethical basis for vaccine mandates because community protection primarily protects unvaccinated people. We contend that the duty to vaccinate is not fundamentally an obligation to make a fair contribution to a public good from which vaccinated people benefit, but a duty to protect the wellbeing of otherwise vulnerable third parties. We flesh out our view by drawing on Martha Nussbaum's capabilities approach. (shrink)