Scottish Government

METHODS AND RESULTS

Economic methods:

The assumptions and methodological approach, cost-benefit analysis are identical to the one used for the scenarios analysed in the initial part of the work (see BTV report). The 'costs' are the costs of preventing BTV8 incursion into Scotland. The 'benefits' are the disease losses thereby avoided. As vaccination may be used in response to incursion, all expenditure on vaccine is included in the benefits i.e. they are part of the disease losses avoided. This means that the lower the 'benefits' the lower the disease losses and the better the control (vaccination) strategy.

Presentation of data supporting conclusions

The incursion scenarios analysed are the ones analysed in the initial report, namely:

1. northwards spread, with BTV arriving in April 2009
2. northwards spread, with BTV arriving in July 2008
3. northwards spread, with BTV arriving in September 2008
4. import of infected animals in April 2009
5. import of infected animals in September 2008

Economic results:

A worthwhile investment in BTV prevention (baseline surveillance costs C ₃) in each scenario should generate sufficient benefits to at least cover the investment costs. This implies that the net present value ( NPV), the expected net benefit ( ENB) ¹ should be positive and the benefit-cost ratio ( BCR) greater than one. In economic terms, the higher the values of NPV, ENB and BCR, the more attractive the investment in the baseline surveillance/prevention costs of BTV. In line with the original final report, Figures 1a to 2b provide the average current discounted benefits (£m) of avoiding BTV incursion for each of the incursion scenarios, (including C6) depending on whether the epidemic is constant through years 3 to 5 (Figure 1a and 1b) or declines (Figure 2a and 2b) and whether a licence is available to move to slaughter (Figure 1b) or not (Figure 2b). Full details including baseline costs, NPV and BCR are tabulated for each incursion scenario in the first report (Commission Number: CR/2007/56). As regards the within incursion scenario analysis for control option C6, CBA indicators (see ANNEX 1c) are of the unweighted (without probabilities of BTV incursion, R) options generated from the economic spreadsheet model for all scenarios using average epidemiological outcomes only (extreme cases, 2.5th and 97.5th percentiles are reported in ANNEX 1.d and ANNEX 1.e respectively).

In the following section, some interpretations of within incursion scenarios (a to e) and the control option C6 are provided in bullet points.

Figure 1a: Current 5-year Discounted Benefits (£m) of avoiding BTV incursions a - e (constant outbreak no slaughter licence)

Figure 1b: Current 5-year Discounted Benefits (£m) of avoiding BTV incursions a - e (constant outbreak with slaughter licence)

Figure 2a: Current 5-year Discounted Benefits (£m) of avoiding BTV incursions a - e (outbreak dies out no slaughter licence)

Figure 2b: Current 5-year Discounted Benefits (£m) of avoiding BTV incursions a - e (outbreak dies out with slaughter licence)

KEY for Figures 1 & 2: Control Option 1 (C1) = 'Do nothing'; Control Option 2 (C2) = Border Protection Zone ( PZ) with 100% vaccination; Control Option 3 (C3) = PZ to Highland B/F Line with 80% vaccination; Control Option 4 (C4) = PZ whole of Scotland with 50% vaccination; Control Option 5 (C5) = PZ of 100km around incursion with 80% vaccination within PZ, Control option (C6) = PZ all Scotland with 80% vaccination

Comparison of within Incursion Scenario CBA Analysis for C6 and C1, C2, C3 C4 and C5

Incursion a (Midge transmission from south in April 2009)

• Scenarios C6a yields the same discounted benefits irrespective of the policy option adopted for move-to-slaughter (with/without license); i.e. the return to baseline surveillance costs C ₃ remains unchanged.
• In comparison with similar incursion scenarios in the initial report, scenario C2a still yields the highest losses if disease occurs.
• Comparing with similar incursion scenarios in the initial report, the best vaccination strategy (lowest disease losses, lowest 'benefits') depends on obtaining a license for movement to slaughter. C4a is best with no license to slaughter while C1a is best with license to slaughter.
• ANNEX1.g gives a breakdown of BTV costs using this incursion scenario with control option C6a as an example. Notice that the direct and indirect costs are not significantly different from the example given in the initial report (i.e. C4a). This implies that mean outcome from the epidemiologic models for C6a and C4a are very similar.

Incursion b (Midge transmission from south in July 2008)

• As in scenarios C6a, scenario C6b yields the same discounted benefits irrespective of the policy option adopted for move-to-slaughter (with/without license); i.e. the return to baseline surveillance costs C ₃ remains unchanged.
• In comparison with similar incursion scenario in the initial report, as in incursion scenario a, scenario C2b is still associated with the highest outbreak losses.
• In comparison with this incursion scenario in the initial report, the best vaccination strategy depends on the duration of the outbreak or the trajectory by which the disease persists after an outbreak as well as on the license position. Scenario C4b gives the best vaccination strategy when BTV lingers and causes losses equivalent to year 2 levels up to year 5. C1b appeared to behave similarly when BTV gradually dies out after year 2 with no licence to slaughter. However, C4b still remains the best vaccination strategy as C1b is the no vaccination option.

Incursion c (Midge transmission from south in September 2008)

• As in scenarios C6a and scenario C6b, scenario C6c yields the same discounted benefits irrespective of the policy option adopted for move-to-slaughter (with/without license); i.e. the return to baseline surveillance costs C ₃ remains unchanged.
• When compared with similar incursion scenarios in the initial report, scenario C2c is associated with the highest outbreak losses.
• As in scenario a, the best disease control option depends on obtaining a license for movement to slaughter. C4c and C6a are almost the same and give the lowest outbreak losses with no license to slaughter while there is little to separate C1c, C4c and C6c and they give lowest outbreak losses with license to slaughter.

Incursion d (Animal import April 2009)

• It is interesting to note that there is almost no difference between C4 and C6 i.e. the advantages of greater vaccine coverage under C6 must be about the same as the extra costs. This means that either C4 or C6 are the best vaccination options under this scenario
• In comparison with this incursion scenario in the initial report, scenario C2d is associated with the highest outbreak losses.
• The lowest outbreak losses still remained scenario C1d for all treatment options.
  

Incursion e (Animal import September 2008)

• Again, there is almost no difference between C4 and C6 returns.
• As in scenario a, b, c and d, scenario C2e is associated with the highest outbreak losses.
• As in scenario d, the lowest avoided disease losses appeared not to be influenced by license for move-to-slaughter or the time trajectory of the disease when an incursion occurs. The (best) vaccination strategy with the lowest disease losses still remained to be C5e.

Sensitivity Analysis

The sensitivity analysis addresses the presence of uncertainty in the CBA based on the key assumed parameters adopted. In essence, sensitivity analysis proposes "what if" scenarios by manipulating certain variables to determine minimum and maximum values of the analytic measures. In this way, the CBA becomes more robust concerning any challenges to its original assumptions. Sensitivity analysis was conducted for the most uncertain parameters used in the CBA analysis. Sensitivity analysis was conducted for changes of ±2% and ±5% for the following parameters: weight loss; milk loss; fertility loss; wool loss; export multipliers for cattle and sheep; own-price elasticities for sheepmeat, beef and milk.

The 'means' & 'q97.5' & 'q2.5' CBA:

The sensitivity analysis indicated no change in the CBA ratios for all the three cases (means, q97.5, q2.5) when changes of ±2% and ±5% were applied for weight loss, milk loss, fertility loss and wool loss. Again, no change in the CBA ratios when changes of ±2% were applied for export multipliers for cattle and sheep and own-price elasticities for sheepmeat, beef and milk. However, the sensitivity analysis showed a change of ±1% in the CBA ratios when export multipliers for cattle and sheep and own-price elasticities for sheepmeat, beef and milk were varied by ±5%.

Summary of results

Economics Outputs

• Economic analysis is based primarily on the average discounted benefits of avoiding BTV8 in Scotland due to baseline surveillance costs.
• As was the case for the initial analysis, it was not possible to estimate the probability of incursion under each scenario modelled because the epidemiologists did not believe sufficient information was available to make such estimates.
• As in the original final report, control option C2 (border PZ, 100% vaccinated) was associated with highest disease incursion losses when compared with all the other control strategies, including C6.
• In most cases the returns of C6 and C4 are almost identical. As C4 was the best vaccination strategy reported in the initial final report, this means that raising vaccination levels from 50% to 80% provides no great advantage (or disadvantage).
• Sensitivity analysis showed no major impacts on the cost benefit analysis results after ±5% change in key assumptions.

CONCLUSIONS

The addition of control strategy C6 to the set of control options does not change the conclusions and recommendations given in the analysis in the initial report. In other words, raising uptake of vaccination from 50% to 80% for a PZ covering the whole of Scotland offered no substantive advantage or disadvantage. The benefits of extra coverage must approximately match the added costs. Given the uncertainties surrounding most aspects of this analysis the higher level of uptake may therefore be considered prudent.

Though not exactly comparable to results of the initial report, the extreme epidemiological outputs (in this case 97.5 ^th, 2.5 ^th percentile) made little difference to the economic assessment of alternative incursion control options based on average epidemiological outcomes. This combined with the results of the sensitivity analysis and the consistency between incursion scenarios is reassuring as it suggests that choice of best control option are more robust to the nature and extent of the incursion than might have been expected.