Try the following document for answers to a number of your questions.
This FAO document clearly states that the main risk arises from domestic poultry with special emphasis on poorly managed live bird markets that can act as “reservoirs” of infection, non-biosecure poultry farming (i.e. smallholder and village poultry in much of Aisa) and domestic ducks that can be infecte,d not show signs of disease and excrete virus for a week or two.
The situation remains that most of the spread of H5N1 HPAI has been associated with the poultry industry especially in places where the virus is endemic.
Wild birds have almost certainly been involved in some of the long distance spread of virus recently (genetic evidence supports this as well), but that once established in a region, spread via poultry or items used with poultry will occur. Iif the disease is not rapidly controlled this becomes the main route of transmission.
You are right to point out that vaccination should be accompanied by appropriate surveillance. However it is also important to recognise that vaccination was used as a response to endemic infection – it was not the initial cause. Vaccination was used in China, Viet Nam and Indonesia only after it was apparent that the disease was out of control and widespread – and the methods that work when a disease is identified early and in a small area, such as depopulation, were no longer feasible.
To eliminate the disease in places such as Viet Nam it is likely that virtually all of the small holder and live poultry marketing sector would have to be shut down for a considerable period of time, which would affect the livelihood of some 13 million poor households and many others involved in this trade. Vaccination is being used to reduce the levels of virus excretion as a prelude to implementation of changes to the way that poultry are raised.
Put simply, the disease cannot be eradicated from Asia unless or until there are major changes in the way that poultry are reared (or the virus changes to something more benign). The socio-economic implications of this are enormous and vaccination will be required as one of the control measures for some time.
I can assure you that without vaccination the situation in Asia would be much worse than it is today.