Thailand and Viet Nam have both experienced several epidemic waves of HPAI H5N1 between 2004 and 2005. The situation in the two countries is particularly interesting to compare because they applied different control strategies, succeeded in temporarily controlling the virus, and faced periodic re-occurrences (Figure 1). Viet Nam undertook massive, repeated vaccination campaigns in combination with other control measures. Thailand has not applied vaccination and placed emphasis on early detection, prevention of poultry movements in high risk areas, including pre-movement testing, and transformation of the freeranging duck production sector. It is difficult to assess whether the re-occurrences experienced by both countries resulted from local persistence of the virus or from new introductions, but recent results suggest that Southeast Asia may constitute a regional ‘evolutionary sink’ for HPAI H5N1 virus, supporting the notion that the region faces periodic reintroductions.
