Publications des agents du Cirad


Financial evaluation of vaccination strategies against highly pathogenic avian influenza

Peyre M.I., Desvaux S., Phan Dang T., Rossi V., Renard J.F., Vu Dinh Tuan, Roger F.. 2008. In : International Conference on Avian Influenza, Bangkok, Thailand, January 23-25, 2008. s.l. : s.n., 1 p.. International Conference on Avian Influenza, 2008-01-23/2008-01-25, Bangkok (Thaïlande).

Introduction: Highly Pathogenic Avian Influenza (HPAI) caused by H5N1 virus has become endemic in some developing countries and millions of birds have been culled with large economical and sociological impacts. Since the end of the first vaccination campaign in Vietnam limited outbreaks in non-vaccinated domestic poultry have been reported. However, the virus is still circulating as confirmed by passive surveillance, targeted active monitoring programs and recent outbreaks. Vaccination is a useful tool to be used to control the disease, but its efficacy could be limited and its application costly according to the choice of the strategy (i.e. targeted versus mass vaccination). The cost and benefit values of different strategies needs to be addressed at national but also local levels, where implementation is decided. Models have been widely used in human health to compare the benefit versus the cost of different vaccination strategies against infectious diseases. Few models on the evaluation of animal diseases vaccination strategies are currently available. In this study we have designed a stochastic model to evaluate the financial outcome of different HPAI vaccination strategies at local levels where they are implemented. Material/Methods: Cost and outcome of a vaccination campaign depend on the vaccination coverage rate, the size of the flock and the risk faced. The choice of a vaccination strategy depends on the epidemiological context and is function of the available vaccine type, the targeted species and the targeted poultry production sector. The stochastic models presented here are based on data from a field study carried out in 2 provinces in Vietnam. Questionnaires and semi-structured interviews were used to collect data at farm, commune, district and province levels from North and South Vietnam in order to parameter the model. The model could be divided in three parts: l) a financial component which evaluates the benefit and cost of HPAI vaccination at the different levels; 2) a dynamic component which estimates the evolution of the vaccination coverage according to the population dynamic at the different levels; 3) a societal component which integrates the perception of the actors and enables the comparison of different vaccination strategies according to different policies and scenarios. Simple prototype models were used to characterise the population dynamic and the social aspects. Those components could be further optimised by integrating more complete models which are currently under development. Results/Perspectives: This model should help policy makers to identify the potential limits of current vaccination strategies both in terms of incentives for the implementers and protective coverage levels. The model could also enlighten which variable has the most impact on the outcome of the strategy, in order to improve it. The flexibility of the model should enable us to transfer it from one socio-economical context to another. The final goal would be to extrapolate and validate this model within an African country and to compare the outcome of various policies according to different epidemiological contexts. (Texte intégral)...

Mots-clés : influenzavirus aviaire; vaccination; analyse des coûts; modèle mathématique; grippe aviaire

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