Typhoid fever has long established itself endemically in rural Ghana despite the availability of cheap and effective vaccines. We used a game-theoretic model to investigate whether the low vaccination coverage in Ghana could be attributed to rational human behaviour. We adopted a version of an epidemiological model of typhoid fever dynamics, which accounted not only for chronic life-long carriers but also for a short-cycle transmission in the immediate environment and a long-cycle transmission via contamination of the water supply. We calibrated the model parameters based on the known incidence data. We found that unless the (perceived) cost of vaccination is negligible, the individually optimal population vaccination rate falls significantly short of the societally optimal population vaccination rate needed to reach herd immunity. We expressed both the herd immunity and the optimal equilibrium vaccination rates in terms of only a few observable parameters such as the incidence rate, demographics, vaccine waning rate and the perceived cost of vaccination relative to the cost of infection. This allowed us not to rely on other uncertain epidemiological model parameters and, in particular, to bypass uncertainties about the role of the carriers in the transmission.

中文翻译：

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加纳农村地区伤寒的高流行可能源于最佳的自愿疫苗接种行为


尽管有廉价有效的疫苗，但伤寒症长期以来一直在加纳农村地区流行。我们使用博弈论模型来调查加纳的低疫苗接种覆盖率是否可以归因于人类的理性行为。我们采用了伤寒动态流行病学模型，该模型不仅考虑了慢性终身携带者，还考虑了直接环境中的短周期传播和通过供水污染进行的长周期传播。我们根据已知的发生率数据校准了模型参数。我们发现，除非（感知的）疫苗接种成本可以忽略不计，否则个体最佳人群疫苗接种率明显低于达到群体免疫所需的社会最佳人群疫苗接种率。我们仅根据一些可观察的参数来表达群体免疫和最佳平衡疫苗接种率，例如发病率、人口统计、疫苗减弱率以及相对于感染成本的感知疫苗接种成本。这使我们能够不依赖其他不确定的流行病学模型参数，特别是绕过关于携带者在传播中的作用的不确定性。