UMR1300 Bio-agression, épidémiologie et analyse de risque, INRA, ENVN, Atlanpole-Chantrerie, Nantes, France.
Prev Vet Med. 2010 Mar 1;93(4):265-75. doi: 10.1016/j.prevetmed.2009.11.004. Epub 2009 Dec 22.
Control strategies of infectious diseases at a regional level can rely on vaccination. When the decision to vaccinate is made by each farmer on a voluntary basis, a farmer vaccinates to protect his own herd. If the vaccinated herds are protected against infection, the risk for other herds is reduced, creating a positive externality (i.e. an impact on a third party not directly involved in the decision). The objectives of this study are to evaluate the effectiveness at a regional level of voluntary vaccination and to analyse the effect of financial incentives and compensation for losses due to disease considering the externalities due to vaccination. We developed a dynamic deterministic model, based on a decision model interacting with an epidemiological state transition model. It determines the proportion of farmers who vaccinate over time, and the evolution of the prevalence of infected herds in a population of herds exposed to the same risk. The behaviour of farmers is modelled assuming perfect information (farmers are fully informed about prevalence, costs of disease and costs of vaccination). The decision to vaccinate is made according to a rational economic behaviour: farmers make their choices to maximize their expected utility, considering their risk aversion. The expected utility is calculated with a decision tree. The epidemiological model is based on a SIR (Susceptible, Infectious, Recovered) model modified to consider imperfect vaccination that protects herds for one year. The model is studied analytically and by simulation. For simulations, we define the epidemiological parameters of the model (transmission rate and average duration of the infectious and recovered states), the herd level effectiveness of the vaccination, the cost of vaccination, the reduction of income due to the disease, the incomes of the farmers and the risk aversion of the farmers. These parameters are based on an endemic disease, BVD (Bovine Viral Diarrhoea). The model shows that voluntary vaccination cannot eradicate the modelled disease. Risk aversion of farmers leads to a lower prevalence at the equilibrium than when farmers are risk neutral. Incentives for vaccination decrease the prevalence but do not result in eradication of the disease. Compensating for disease losses in newly infected farms leads to an increase in prevalence, due to moral hazard (farmers behave less carefully than if they were fully exposed to the risk), except if it is restricted to vaccinated herds.
区域级传染病的控制策略可以依靠疫苗接种。当每个农民自愿做出接种决定时，农民会为保护自己的畜群而接种疫苗。如果接种疫苗的畜群免受感染，那么其他畜群的风险就会降低，从而产生正外部性（即对未直接参与决策的第三方的影响）。本研究的目的是评估自愿接种疫苗在区域层面的效果，并分析在考虑到疫苗接种产生的外部性的情况下，对因疾病造成的损失给予经济激励和补偿的效果。我们开发了一个动态确定性模型，该模型基于与流行病学状态转换模型相互作用的决策模型。它确定了随着时间的推移接种疫苗的农民比例，以及暴露在相同风险下的畜群中感染畜群的流行率的演变。假设农民拥有完美信息（农民充分了解疾病的流行率、成本和疫苗接种成本）来模拟农民的行为。根据理性经济行为做出接种疫苗的决策：农民根据他们的风险厌恶程度，使他们的选择最大化他们的预期效用。预期效用是通过决策树计算的。流行病学模型基于一个 SIR（易感者、感染者、康复者）模型，该模型经过修改以考虑保护畜群一年的不完全疫苗接种。该模型通过分析和模拟进行研究。对于模拟，我们定义了模型的流行病学参数（传播率和感染和康复状态的平均持续时间）、疫苗接种对畜群的有效性、疫苗接种成本、疾病造成的收入减少、农民的收入和农民的风险厌恶程度。这些参数基于一种地方病 BVD（牛病毒性腹泻）。模型表明，自愿接种疫苗不能根除所模拟的疾病。农民的风险厌恶导致均衡时的流行率低于农民风险中性时的流行率。接种疫苗的激励措施会降低流行率，但不会导致疾病的根除。对新感染农场的疾病损失进行补偿会导致流行率增加，这是由于道德风险（如果农民完全暴露于风险之中，他们的行为就不会那么谨慎），除非将其仅限于接种疫苗的畜群。
