International animal health experts are debating whether vaccinating chickens against the bird flu is the best way to limit the current spread of the virus in Asia or to prevent future outbreaks. The scientific community is divided on the issue.
Here in Hong Kong, chicken vendors are still selling live poultry. But unprecedented bird flu outbreaks across much of Asia have caused countries to ban chicken imports, close markets and cull tens of millions of birds.
Hong Kong has so far been spared the outbreak. But the territory was plagued with the same strain of flu in 1997, when it jumped to humans for the first time. The government responded by culling every chicken and instituting new health measures.
Some experts say this is why Hong Kong chickens now are still healthy, having been given a general vaccine against avian influenza.
However, Dr. Hans Wagner, a senior expert at the Food and Agriculture Organization in Bangkok, says not all experts agree that vaccinating chickens is a good idea.
"There's a lot of discussion regarding vaccination against avian influenza," he said. "There are pros and cons and the scientific world is divided. The position up to now [is] that we should avoid vaccination."
He says most experts seem to agree that culling all farm birds - sick or not - is the best way to end an outbreak.
Dr. Wagner advises that while vaccines can offer some protection against the current bird flu virus, it might not protect against a similar strain later on. He says outbreaks can easily reemerge if contaminated birds are kept alive.
Dr. Natalie Dillon is a microbiologist with DNA CHIPS, a Hong Kong-based company that makes bird flu test kits.
She agrees vaccination during an epidemic is a bad solution because vaccinated poultry can still contract and spread the virus without showing symptoms of the disease.
"All the vaccinated chickens can be possible carriers," she said. "They can have the active virus in their body and they can pass this on, causing a great problem to other countries and other birds that have not been vaccinated and potentially even humans."
Some animal health experts oppose the vaccine altogether, even when it is used as a preventative measure after bird flu outbreaks have subsided.
They argue that the bird flu vaccine is expensive, distributing it across Asia would be impossible and it does not protect against emerging future strains of the virus.
In the pro camp, scientists argue the threat posed to poultry if they are not vaccinated far outweighs the problems of the vaccine.
Dr. Graham Laver in is an influenza expert who helped develop the anti-viral flu drug known commercially as Tamiflu in Canberra, Australia.
"If the whole country has experienced bird flu, it doesn't matter if you've got a few carriers, because you are no worse off and you may save quite a lot of birds from death," said Graham Laver.
Some theories have surfaced in recent days that chickens in southern China were the source of the outbreak.
Bird flu was present in China in early 2003. Two members of a Hong Kong family visiting Fujian Province were infected with the H5N1 virus after close contact with chickens. They died after returning to Hong Kong for treatment.
A British science magazine, New Scientist, theorizes that the virus could have spread undetected in China from vaccinated poultry to non-vaccinated farm and wild birds.
While the virus is deadly in many farm birds, its threat to humans, so far, is limited. People can catch it after handling infected birds, but this is still rare. Scientists, however, fear the virus could threaten human health globally if it begins to spread between people.
Health experts will gather in Rome next week to debate the use of the poultry vaccine in dealing with future and present threats of the bird flu.