While most Asian countries are better prepared than they were a year ago to prevent or contain the spread of avian influenza, epidemiologists say there is no room for complacency about the virus that remains widespread in the region.

"The concern is still there," said Hans Troedsson, head of the World Health Organisation (WHO) in Vietnam, where after a one-year hiatus bird flu has spread across dozens of farms in six southern provinces in recent weeks.

"What we see an indication of -- not only in Vietnam with the poultry outbreaks, but also with the human cases in China and Indonesia and so on -- is that the virus is still here," he said.

"And it still has the potential capability to change, and to change in the worst scenario into a virus strain that could cause a pandemic through being easily transmitted from human to human."

Asian nations have raised their alert level as four people died of bird flu in Indonesia last week, China and South Korea reported new human infections, and the virus has spread across farms in Vietnam's southern Mekong Delta.

"There is a seasonal pattern of the influenza virus," said Troedsson. "It is more active when it's colder. When the temperature goes down, usually all the respiratory infection viruses get more active.

"People's behaviour during winter time also changes. They spend more time inside homes, and homes are more crowded, so they expose each other to the risk of spreading the virus."

For now, experts say, there is no evidence the lethal virus has mutated to spread easily among humans, and no cause for alarm.

China last week reported its first human case of bird flu in six months, but the farmer who fell ill made a full recovery.

"We need to be vigilant all year round, but this case shouldn't be seen as particular cause for alarm," said WHO spokeswoman Joanna Brent.

"One isolated case in six months is certainly not a sign for worry, and the threat level to humans remains unchanged."

But experts also warn that the risk will increase when China, Vietnam and other Asian countries celebrate the Lunar New Year in mid-February, when the movement of both poultry and people sharply increases.

Migratory birds also continue to pose a risk, warned York Chow, the health secretary of Hong Kong, where a dead wild bird has just tested positive for a milder strain of the bird flu virus.

"This is the real risk that the whole world is facing," Chow said Saturday.

Since bird flu swept from Asia to the Middle East, Europe and Africa last winter, UN agencies and governments have improved surveillance and vaccinations, boosted health services and stockpiled anti-viral drugs.

But gaps remain, both in vaccination drives and in spreading information about the virus to small poultry farmers in many remote Asian regions.

In Indonesia, which last year overtook Vietnam as the worst hit country and has now recorded 61 human deaths, government health official I Nyoman Kandun said education remained the priority in the fight against bird flu.

"The people need to be involved," he said. "It is (the government's) job to package the information such that it is easily understood by everyone.

"Indonesia is vast and we have a culture of keeping poultry and other animals near the home," said Kandun. "This needs to change, or extra precautions need to be practised."

Officials in the archipelago maintain that vaccination drives have proven effective, but they also say they only have enough doses to effectively vaccinate about 10 percent of backyard poultry this year.

In Thailand, disease control chief Thawat Sunthrajarn said there was cause for neither alarm nor complacency, but added that the kingdom was "on high alert after the reported resurgence in Vietnam and China."