As public health leaders from around Asia gathered in Ho Chi Minh City Wednesday (February 23) to kick off a 3-day conference on controlling the spread of avian flu, the World Health Organization (WHO) highlighted the role waterfowl play in spreading the deadly disease.

Shigeru Omi, the Western Pacific regional leader of the World Health Organization, opened the meeting with calls for cooperation between animal and human health experts.

"We at WHO believe that the world is now in the gravest possible danger of a pandemic," Omi said. His speech soon turned to ducks, thought to be the reservoir for the virus. "We now know that domestic ducks are playing a silent role in the transmission of the virus. The ducks are spreading the virus without showing any signs of illness. The public health implications of this are very serious."

Since last winter, bird flu has killed at least 45 people across Thailand, Vietnam, and Cambodia, and fears that it could trigger a human influenza epidemic remain high. It is in this context that the United Nations Food and Agricultural Organization and the World Organization for Animal Health called this week's meeting to evaluate the current avian flu situation and to advise on new control measures.

Just days before the summit was due to begin, two countries at the center of the problem announced significant developments in dealing with the disease.

Host nation Vietnam said it planned to allow testing on people of a newly developed human vaccine against avian influenza by the year's end. It also planned to ramp up efforts of distributing rapid diagnostic kits to the country's far-flung regions.

Vietnam currently relies on surveillance and culling to stamp out outbreaks in chickens and waterfowl, but the measures have failed to protect people from catching the disease. According to statements carried by state-controlled media, the country's National Hygiene and Epidemiology Institute on Monday (February 21) announced that vaccine trials on mice and chickens had proven successful.

A day earlier, Thailand's government had announced it would agree to vaccinating selected healthy poultry against the disease, including roosters bred for cockfighting and chickens kept in pens by small-scale farmers and families. But chickens raised for export at larger farms would not be vaccinated, according to statements. Japan, one of the biggest importers of Thai chicken, does not accept poultry that have been vaccinated against the disease.

As the Vietnamese and Thai decisions show, issues relating to vaccination are not straightforward for countries tackling the avian disease. Until Thailand's recent decision, China, Indonesia, and Pakistan had been the only countries in Asia that officially vaccinated poultry against avian influenza, according to the Food and Agriculture Organization (FAO). Since the start of the year, these countries have not reported avian flu outbreaks in poultry.

But as one FAO official, who preferred to remain unnamed, told The Scientist, vaccination of all poultry is probably unfeasible in many South East Asian countries. "Seeing that we have widespread outbreaks in small-scale [farming]—the backyard chickens—I see it difficult to get a high enough vaccination coverage in order to really curb down the disease."

The problems of poorly matched vaccines are also a concern, said Juan Lubroth, a senior expert in FAO's infection disease group based in Rome, Italy. "There is nothing as dangerous as using an ineffective vaccine, because it gives you a false sense of security."

Lubroth's view is that when administered correctly to all poultry, the avian influenza vaccine can be the best solution to preventing avian flu in chickens and may also lessen the risk of human infection by lowering levels of viral shedding.

"A partial match is good enough to protect animals from death," said Ruben O. Donis from the US Centers for Disease Control and Prevention in Atlanta, Ga., "but from an ecological and public health perspective, this kind of [vaccine mismatch] tends to accelerate the evolution of the virus."

WHO's Omi avoided remarks about animal vaccination on Wednesday. Instead he emphasized improved animal husbandry and the avoidance of traditional "wet markets" where live poultry are kept in cramped cages and in close proximity to different species of waterfowl and farmed animals.

"Together with our member states... we can set out the best practices for the production, distribution, and processing and marketing of animals for food," he said.