As governments and researchers race to develop vaccines against Asia’s deadly bird flu, experts are debating their effectiveness against a versatile and resilient virus.

Vietnam, the country worst hit by the H5N1 strain that has killed 46 people in Asia, is testing vaccines for poultry and humans. The United States is also preparing trials for a human bird flu vaccine.

Thailand, the world’s fourth largest chicken exporter before the epidemic hit last year, this week reversed its opposition to vaccines and approved a limited treatment plan.

There is positive development on all vaccines,” Hans Troedsson, Vietnam representative of the U.N. World Health Organization (WHO), said on the sidelines of a bird flu conference in southern Vietnam’s Ho Chi Minh City.

“If everything goes well, there might be a possibility of having a (human) vaccine available even this year or next year,” he told Reuters.

But he said the virus - which experts fear could mutate into a new, lethal strain that could spread rapidly among humans, killing millions - is very versatile.

“Remembering that of course if the strain changed, the vaccine developed now is the vaccine against the current strain so it might be less protective, but it’s still important,” Troedsson said.

Researchers at Vietnam’s National Institute of Hygiene and Epidemiology last week reported favorable results after testing a human vaccine they made on mice and chickens. Results from monkeys would be known by early March before Vietnam’s vaccine could be tested on humans.

“It looks promising but it’s bit too early to say how successful it could be,” Troedsson said.

MOVING CAREFULLY

Meanwhile, Vietnam is pushing ahead with tests of Chinese and Dutch vaccines in 8,000 chickens scheduled for late this month in the northern province of Ha Tay, outside the capital, Hanoi.

Bui Quang Anh, director of the Agriculture Ministry’s Animal Health Department, said there was no immediate plan to vaccinate chickens and ducks in main poultry-producing provinces, or birds in high-risk areas such as the Mekong Delta, site of Vietnam’s latest outbreaks.

“If the local management is good, it may be possible to apply the vaccine in the fourth quarter of this year,” he said.

Samuel Jutzi of the Rome-based Food and Agriculture Organization (FAO) said vaccines can be one effective tool in an overall strategy against a virus now endemic in parts of Asia.

“It’s a commercial and political decision whether to go for vaccination,” Jutzi said, noting that some countries refuse to accept imports of vaccinated poultry.

The World Organization for Animal Health will consider in May changes to guidelines that would allow trade in vaccinated birds from special zones free of bird flu.

That may encourage affected countries to start vaccination programs, but Bangkok is moving carefully.

Thailand, which lost millions of dollars in exports to Japan and Europe last year, plans to vaccinate backyard chickens, fighting cocks and free-range ducks but not poultry raised for export, Thai newspapers reported this week.