In 2006, the poultry population of Vietnam was about 215 million heads. However, between 2004 and 2008, the Highly Pathogenic Avian Influenza (HPAI) caused by H5N1 virus was broken in affected almost all provinces in Vietnam with millions of birds culled. This had large economical and sociological impacts. A question has been raised: how could Vietnam limit this epidemic? The research aims to identify the poultry production systems with their various constraints, including diseases and to evaluate the cost-benefit impact of a mass vaccination programme implemented from March to August 2007 at local level in Long An Province within the Mekong Delta. Two principal poultry farming systems are characterised: the commercial poultry production system (system 1) with low to moderate bio-security level, and the small-scale production system (system 2) with a low bio-security level. The scenarios of cost-benefit analysis of vaccination campaigns against HAPI caused by H5N1 virus give a good strategy for the restructure of poultry production and farmers' incentives to vaccinate. The vaccination is more cost effective for the farmer than culling operations, with the BCR scenarios are between 31 to 78 times more.