This paper examines a theoretical model designed to characterize a static, individual vaccination decision environment. I identify and characterize both equilibrium and socially optimal vaccination behavior and determine how this behavior changes as the effectiveness of the vaccine changes. I also evaluate the individual and social welfare implications of a change in vaccine effectiveness. I find that under certain conditions, an increase in vaccine effectiveness can decrease the number of agents vaccinating in equilibrium due to the positive external effects of vaccination. Notably, it is also possible for individual and total welfare to decrease. This is an undesirable, and perhaps unexpected, consequence of better vaccines. Fortunately, welfare at the social optimum always increases as vaccine effectiveness increases. However, equilibrium behavior often falls short of the social optimum due to the positive externalities created by vaccinating.

中文翻译：

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疫苗有效性对个人疫苗接种决策和福利的作用

本文研究了一个旨在描述静态、个体疫苗接种决策环境的理论模型。我识别并描述平衡和社会最佳疫苗接种行为，并确定这种行为如何随着疫苗有效性的变化而变化。我还评估了疫苗有效性变化对个人和社会福利的影响。我发现在某些条件下，由于疫苗接种的积极外部效应，疫苗有效性的提高可以减少平衡状态下接种疫苗的人数。值得注意的是，个人和总体福利也有可能下降。这是更好的疫苗带来的不良后果，或许也是意想不到的后果。幸运的是，随着疫苗有效性的提高，社会最佳福利总是会增加。然而，由于疫苗接种产生的正外部性，均衡行为常常达不到社会最优状态。