Our demanding obligations to protect the vulnerable in pandemics vastly surpass what we owe each other in ordinary circumstances. In this paper, I defend the novel explanation that our obligations in public health emergencies are the premium we pay for insuring against a sudden and significant event, of which the current pandemic is just one instance. Since we are all vulnerable, the stakes are significant, and help is urgent in these situations, it is rational pre-pandemic to be part of an ‘informal insurance scheme’ that imposes very demanding obligations in an emergency. This theory explains the discrepancy between the extraordinary and ordinary obligations, why the relatively protected young should bear heavy burdens to protect the vulnerable, and why the primary obligation in a pandemic is to maintain the pre-pandemic status quo, not solve background injustices. Finally, the theory has implications for our changing obligations when pandemics become endemic and frequent.