Vaccination has been accepted as an option for the control of HPAI by the Food and Agriculture Organization of the United Nations and the World Organization for Animal Health. Emphasis is placed on the use of vaccine to facilitate eradication. The continued use of poultry influenza vaccines without an eradication plan has immediate benefits but also long-term consequences. The difficulty with continued vaccine usage is that it promotes genetic variation and allows shedding of virus in the absence of disease signs, thus creating the potential for epicenters of virus spread. Further, while both inactivated oil emulsion whole-virus H5 vaccines and recombinant NDV vaccines containing H5 HAs are highly efficacious in chickens, the recombinant NDV vaccines are less efficacious in ducks. The experience in Vietnam illustrates these points. In 2005, after 61 human cases of HP H5N1 virus infection and 19 deaths, universal poultry vaccination and reduction of duck populations were implemented, with dramatic results. In 2006, there were no human cases of H5N1 influenza. However, in 2007-2008, there were 14 human cases of HP H5N1 virus infection and 10 deaths (http://www.who.int/ csr/disease/avian_influenza/country/cases_table_2009_03_11/ en/index.html). The difficulty of controlling H5N1 HPAI viruses in ducks by vaccination and the enormous task of vaccinating sufficient poultry to maintain ''herd immunity'' remain daunting obstacles.