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This paper explores the implications for public policy of the fact that individuals have incomplete but private information about their exposure to infectious disease when they make migration decisions. In a 2-period model we study conditions under which the presence of quarantine measures may lead to inefficient outcomes by strengthening individuals' interest in migration to escape centres of disease and thereby imposing negative externalities on other uninfected individuals. We show first that when the disease has an epicentre, the marginal migrant imposes a net negative externality. Secondly, quarantine policies may sometimes encourage migration instead of discouraging it. Thirdly, even when they succeed in discouraging migration, quarantine policies may lower social welfare, and even increase overall disease incidence, if they go too far, thereby discouraging those intra-marginal migrants for whom private benefits exceed private costs by more than the negative externality they impose on others.

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