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Vaccination against foot-and-mouth disease: do initial conditions affect its benefit?

Porphyre T, Auty HK, Tildesley MJ, Gunn GJ, Woolhouse ME - PLoS ONE (2013)

Bottom Line: 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.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.However, if a decision to vaccinate is made, we show that delaying its implementation in the field may markedly reduce its benefit.

View Article: PubMed Central - PubMed

Affiliation: Epidemiology Group, Centre for Immunity, Infection and Evolution, University of Edinburgh, Ashworth Laboratories, Edinburgh, United Kingdom.

ABSTRACT
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.

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Influence of Ri on the benefit of the vaccination policy.Spatial distribution of the farm-level basic reproductive ratio, Ri (A) and its relation with the FMD vaccination benefit (VB) in Scotland. Vaccination benefit was measured based on the number of infected premises (B) and the epidemic duration (C) in the situation where 1 premise was infected at first detection (early detection). Values of Ri show in B and C are the average across all farms in each county. Note also that county-level estimates in B and C were grouped into the two areas as defined in this study (Figure 2). The colour scale used in the map shows the average value in a 5 × 5 km grid lattice. Estimates of Ri were computed based on the Scottish Agricultural Census June 2011 and using the method described in [15]. Solid curve in B and C represents the smooth fit to better visualize trends in the data set. The fit was generated using the locally weighted scatter plot smoother (LOWESS) method.
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pone-0077616-g004: Influence of Ri on the benefit of the vaccination policy.Spatial distribution of the farm-level basic reproductive ratio, Ri (A) and its relation with the FMD vaccination benefit (VB) in Scotland. Vaccination benefit was measured based on the number of infected premises (B) and the epidemic duration (C) in the situation where 1 premise was infected at first detection (early detection). Values of Ri show in B and C are the average across all farms in each county. Note also that county-level estimates in B and C were grouped into the two areas as defined in this study (Figure 2). The colour scale used in the map shows the average value in a 5 × 5 km grid lattice. Estimates of Ri were computed based on the Scottish Agricultural Census June 2011 and using the method described in [15]. Solid curve in B and C represents the smooth fit to better visualize trends in the data set. The fit was generated using the locally weighted scatter plot smoother (LOWESS) method.

Mentions: Exploring the reasons for such a pattern, we compared the average estimate of VB for epidemics starting in each county with county-level variables informing on the farm industry, namely the cattle and sheep densities (in heads per km2) and the number of sheep per head of cattle. We examined also the correlation between VB and the average farm-level basic reproductive ratio Ri computed as in [15] (Figure 4A). Whilst Ri is correlated with cattle density and sheep density (Spearman rank statistic =0.46 and 0.73), it is also influenced by other factors relating to the underlying herd structure such as production type (i.e. whether herd is cattle only, sheep only, or mixed herd), herd size and density of premises, and to the characteristics of the virus strain (Equations 1-3). Although cattle and sheep densities were significantly correlated with the VB computed based on the number of IPs and duration of epidemics, there was a closer correlation (Spearman rank statistic =0.79 and 0.75), as well as a better fit, between VB and Ri (Figures S3-S4). Figure 4B and 4C show the variation of VB with the number of IPs and the duration of epidemics starting in each county as a function of Ri averaged across all farms present in the county of incursion. Clearly, higher values of Ri yield higher values of VB.


Vaccination against foot-and-mouth disease: do initial conditions affect its benefit?

Porphyre T, Auty HK, Tildesley MJ, Gunn GJ, Woolhouse ME - PLoS ONE (2013)

Influence of Ri on the benefit of the vaccination policy.Spatial distribution of the farm-level basic reproductive ratio, Ri (A) and its relation with the FMD vaccination benefit (VB) in Scotland. Vaccination benefit was measured based on the number of infected premises (B) and the epidemic duration (C) in the situation where 1 premise was infected at first detection (early detection). Values of Ri show in B and C are the average across all farms in each county. Note also that county-level estimates in B and C were grouped into the two areas as defined in this study (Figure 2). The colour scale used in the map shows the average value in a 5 × 5 km grid lattice. Estimates of Ri were computed based on the Scottish Agricultural Census June 2011 and using the method described in [15]. Solid curve in B and C represents the smooth fit to better visualize trends in the data set. The fit was generated using the locally weighted scatter plot smoother (LOWESS) method.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3815046&req=5

pone-0077616-g004: Influence of Ri on the benefit of the vaccination policy.Spatial distribution of the farm-level basic reproductive ratio, Ri (A) and its relation with the FMD vaccination benefit (VB) in Scotland. Vaccination benefit was measured based on the number of infected premises (B) and the epidemic duration (C) in the situation where 1 premise was infected at first detection (early detection). Values of Ri show in B and C are the average across all farms in each county. Note also that county-level estimates in B and C were grouped into the two areas as defined in this study (Figure 2). The colour scale used in the map shows the average value in a 5 × 5 km grid lattice. Estimates of Ri were computed based on the Scottish Agricultural Census June 2011 and using the method described in [15]. Solid curve in B and C represents the smooth fit to better visualize trends in the data set. The fit was generated using the locally weighted scatter plot smoother (LOWESS) method.
Mentions: Exploring the reasons for such a pattern, we compared the average estimate of VB for epidemics starting in each county with county-level variables informing on the farm industry, namely the cattle and sheep densities (in heads per km2) and the number of sheep per head of cattle. We examined also the correlation between VB and the average farm-level basic reproductive ratio Ri computed as in [15] (Figure 4A). Whilst Ri is correlated with cattle density and sheep density (Spearman rank statistic =0.46 and 0.73), it is also influenced by other factors relating to the underlying herd structure such as production type (i.e. whether herd is cattle only, sheep only, or mixed herd), herd size and density of premises, and to the characteristics of the virus strain (Equations 1-3). Although cattle and sheep densities were significantly correlated with the VB computed based on the number of IPs and duration of epidemics, there was a closer correlation (Spearman rank statistic =0.79 and 0.75), as well as a better fit, between VB and Ri (Figures S3-S4). Figure 4B and 4C show the variation of VB with the number of IPs and the duration of epidemics starting in each county as a function of Ri averaged across all farms present in the county of incursion. Clearly, higher values of Ri yield higher values of VB.

Bottom Line: 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.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.However, if a decision to vaccinate is made, we show that delaying its implementation in the field may markedly reduce its benefit.

View Article: PubMed Central - PubMed

Affiliation: Epidemiology Group, Centre for Immunity, Infection and Evolution, University of Edinburgh, Ashworth Laboratories, Edinburgh, United Kingdom.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus