Vaccination against Foot-And-Mouth Disease: Do Initial Conditions Affect Its Benefit?

When facing incursion of a major livestock infectious disease, the decision to implement a vaccination programme is made at the national level. To make this decision, governments must consider whether the benefits of vaccination are sufficient to outweigh potential additional costs, including further trade restrictions that may be imposed due to the implementation of vaccination. However, little consensus exists on the factors triggering its implementation on the field. This work explores the effect of several triggers in the implementation of a reactive vaccination-to-live policy when facing epidemics of foot-and-mouth disease. In particular, we tested whether changes in the location of the incursion and the delay of implementation would affect the epidemiological benefit of such a policy in the context of Scotland. To reach this goal, we used a spatial, premises-based model that has been extensively used to investigate the effectiveness of mitigation procedures in Great Britain. The results show that the decision to vaccinate, or not, is not straightforward and strongly depends on the underlying local structure of the population-at-risk. With regards to disease incursion preparedness, simply identifying areas of highest population density may not capture all complexities that may influence the spread of disease as well as the benefit of implementing vaccination. However, if a decision to vaccinate is made, we show that delaying its implementation in the field may markedly reduce its benefit. This work provides guidelines to support policy makers in their decision to implement, or not, a vaccination-to-live policy when facing epidemics of infectious livestock disease.

当重大牲畜传染性疫病发生入侵时，疫苗接种计划的实施决策由国家层面统筹制定。为作出该决策，政府需权衡疫苗接种的收益是否足以覆盖潜在额外成本，其中包括因实施疫苗接种可能招致的后续贸易限制措施。然而，目前学界尚未就田间触发该政策实施的各类影响因素达成广泛共识。本研究以口蹄疫（foot-and-mouth disease）疫情为场景，探讨了多项触发因素对该应急活疫苗接种政策实施效果的影响。具体而言，我们以苏格兰为研究场景，检验了疫病入侵点位变化与接种实施延迟是否会影响该政策的流行病学收益。为达成该研究目标，我们采用了在英国广泛用于评估疫病防控措施有效性的空间养殖场址模型（spatial, premises-based model）。研究结果表明，是否实施疫苗接种并非简单易决的问题，其决策结果很大程度上取决于受威胁畜群的本地潜在种群结构。就疫病入侵防控准备工作而言，仅识别畜群密度最高的区域，可能无法涵盖所有可能影响疫病传播及疫苗接种收益的复杂因素。但倘若已作出疫苗接种决策，本研究证实田间接种实施的延迟将显著降低该政策的收益。本研究可为政策制定者在遭遇牲畜传染性疫病疫情时，就是否实施应急活疫苗接种政策提供决策参考依据。