Asia still has a chance to beat the spread of bird flu among humans despite fears the deadly virus may mutate into a stronger form that people can pass to each other, the World Health Organisation said.

The bird flu crisis, which has killed or prompted the slaughter of millions of poultry across Asia, has officially caused the death of 12 people.

"We have no pandemic, we have very few cases, there is no indication whatsoever of ... any widespread large outbreak caused by this outbreak in humans," said Klaus Stoehr, head of the WHO's global influenza programme.

Most of the human fatalities -- nine in Vietnam and three in Thailand -- are thought to have been caused by contact with an infected bird.

But there are fears that two dead Vietnamese sisters could have become the first case of human-to-human transmission of the virus.

"Things are still in the box. It has not come out. If we sit on the lid it will stay there and we still have that window of opportunity open," Stoehr told a telephone news conference from the WHO's Geneva-based headquarters.

Bird flu mutated into a form transmittable by humans during an outbreak in Hong Kong in 1997, but the second-generation strain was very mild and failed to generate a public health emergency, the doctor explained.

The United Nations' health body has warned this time that millions of people around the world could die if the H5N1 strain of bird flu became a deadly version transmittable between humans.

"In essence we could have a very rapid emergence of a completely new virus which could spread like a normal influenza virus," said Stoehr.

"Another scenario we have is that the avian virus would gradually change over time and we would have a gradual increase in human-to-human transmission," he added.

The fact that just a handful of human cases have been reported to-date despite the bird flu being around for several weeks was fairly encouraging.

"We believe we might only be seeing the tip of the iceberg," Stoehr warned, but he noted that other cases may go unreported as they are so mild.

"This is ... taking a little bit away from the worry that we have," he said.

It "would reconfirm that we believe we have a possibility to deal with this avian outbreak before this virus gets a foothold in humans, provided we can eliminate the animal reservoir in a safe way that humans are not going to be exposed anymore," he said.

Three drug companies have pledged to donate 220,000 doses of normal flu vaccines to help protect people exposed to the crisis, and the authorities in Thailand have said they would like to receive them, according to Stoehr.

The WHO has advised people involved in culling poultry to wear protective clothing, to be vaccinated against human influenza and wash their hands frequently to reduce the risk of catching bird flu.

In a separate twist, German health authorities said they were examining a woman recently returned from Thailand in a suspected case that could be Europe's first human incident of avian influenza in the current outbreak.

World experts on bird flu were due to meet in Rome Tuesday to plot a strategy for controlling the disease, a UN Food and Agriculture Organisation (FAO) source said Friday.

Specialists from the World Health Organisation, World Organisation for Animal Health and the Rome-based FAO are to convene at the FAO headquarters from Tuesday until Thursday.

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