The recent scientific report of the European Food Safety Authority (EFSA) on Sheep and Goat Pox (SGP) in Greece and Bulgaria records significant limitations regarding the ability to draw safe conclusions about the implementation of vaccination in Greece.
Already in the methodological section, EFSA noted that the attempt to apply the same mathematical model used for Bulgaria did not yield reliable results for the Greek case.
As stated, “ the preliminary analysis of outbreak data using the same methods failed to produce reliable estimates for the kernel parameters,” even “ when the analysis was restricted to spatially and temporally limited datasets reflecting different epidemic clusters.”
According to the report, the initial simulations showed that simple distance-based models cannot capture the dynamics of the disease in the country. As noted, “ initial simulations of spread across the whole of Greece showed that a simple distance-based kernel model cannot easily account for the natural barriers to disease spread arising from mountainous areas and the numerous islands.”
For this reason, EFSA explicitly clarified that “ the kernel-based model was not used further to investigate the spread of SGP or the impact of vaccination in Greece.” The report explains that a reliable simulation of the Greek situation would require a different approach and additional data.
It stated that “ modelling the Greek situation would require detailed animal movement data and the construction of a more complex model,” which, as emphasised, “ was not feasible within the time frame allocated for this assessment.”
As a result, “ the evaluation of vaccination scenarios for Greece was based on a descriptive spatio-temporal analysis of the epidemiological data.” This descriptive analysis records that the epidemic in Greece is characteried by an “ extensive geographical and temporal scale” and by “ multiple epidemic clusters.”
EFSA reported that “ ten spatio-temporal clusters” were identified across the country, and notes that “ the presence of clusters far apart from each other across the country suggests that there were long-distance movements of infected animals.”
With regard to vaccines, EFSA clarified the regulatory framework within which the assessment operates. As stated in the chapter on the interpretation of the terms of reference, “ at present, there are no SGP vaccines approved in the European Union,” and it is underlined that “ EFSA experts do not carry out vaccine evaluations that could lead to a recommendation of a veterinary medicinal product.”
The report is based on a literature review and on experimental data from the European Union Reference Laboratory (EURL), but it recognizes limitations in the quality of the available evidence.
As noted, “ many studies were small-scale, lacked detailed reporting of the quantitative effects of vaccines, or were available only as abstracts,” which, according to EFSA, “ limits the assessment of the risk of bias and the potential for generalization.”
In the section on vaccine safety, it is also pointed out that “ certain strains, overdosing, stress, breed susceptibility, or improper administration can cause some adverse reactions,” while it is noted that the available vaccines “ do not have a DIVA mechanism (Differentiating Infected from Vaccinated Animals).”
In contrast to Bulgaria, for which EFSA presents mathematical simulation results showing that rapid detection and culling of infected holdings can bring the epidemic under control within 1-2 years, for Greece the report itself avoids a quantitative assessment of the impact of vaccination.
The reason, as emerges from the text, is the inability to apply a reliable spread model under Greek conditions.
Overall, the EFSA report clearly records that, for Greece, the assessment of management options for sheep and goat pox is based exclusively on descriptive data and that the available scientific tools did not allow the drawing of quantitative conclusions on the implementation and effectiveness of a large-scale vaccination strategy.
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