"Early detection is the first line of defence in defeating the virus but Indonesia and Vietnam, which do not have enough resources and adequate organisation, were late in responding to bird flu," Vallat told Reuters during a visit to South Korea.

"They cannot manage this virus by just killing animals at this stage. It is too late. The solution is using vaccination."

Bird flu has been confirmed as the cause of 64 deaths in Asia since late 2003. Most human cases have been blamed on direct or indirect contact with infected chickens.

The highly pathogenic H5N1 strain is endemic in poultry in some parts of Asia but cannot pass between people, though experts fear it could mutate into a form that does.

"The problem is money. Indonesia and Vietnam are the top priorities which need global help," Vallat said.

Vietnam would need around $150 million in international aid to fight bird flu, a senior government official told Reuters last week. So far the country has received $10 million from donors including the United States, China and the Netherlands. Indonesia has said it wants grants, not loans, to fight the virus.

WINDOW OF OPPORTUNITY

Vallat said a window of opportunity existed to reduce the risk of a human pandemic by limiting the spread of bird flu among chickens and ducks.

"The best way to prevent a pandemic is to reduce or eliminate the virus from the animal source," he said.

In many parts of Asia, poultry live side-by-side with people, increasing the chances of humans becoming infected with bird flu.

Teams of volunteers, soldiers and students will make door-to-door tests of backyard chickens in Indonesia next month. The UN Food and Agriculture Organisation has sent an emergency team to Indonesia that will spearhead testing across Java.

Vallat also said, for early detection and culling to work, a carrot-and-stick approach should be used, meaning poultry farmers should be given financial compensation for destroying infected flocks and penalised for keeping sick birds.

"Rapid and early reponse is very important. Laboratory work takes three days. Bird flu can spread all over the country in just three days."

Vietnam is accelerating the slaughter of poultry in its two largest cities as it tries to stop the spread of bird flu, which has killed 42 people in the country and infected more.

Indonesia has had five confirmed human deaths from the H5N1 strain of bird flu. Local tests have shown two others have died, although those results have yet to be confirmed by a Hong Kong laboratory affiliated with the World Health Organisation.

Thirteen have died in Thailand and four in Cambodia.

Vallat said China should be able to stamp out bird flu, although the huge size of the country could make this difficult to achieve in a short period of time.

"They have a strong political willingness to control bird flu. They are better prepared than before," he said.