World Health Organisation experts helping Vietnam to battle a recurrence of bird flu said governments should be cautious about prematurely announcing they had beaten the disease, which has killed 27 people this year.

“A long timeframe is necessary because even if countries are successful in controlling the disease in their own country, they ought to check the borders with other countries where the disease still exists and there is also the issue of migrating birds”, said Peter Horby, a Hanoi-based WHO medical epidemiologist.

Horby was speaking on behalf of a WHO team of three experts, including two Manila-based staff, who are helping the Southeast Asian country investigate the latest outbreak of the H5N1 strain of avian flu, which killed three people this month.

Earlier this year, the virus rampaged through much of Asia, killing 16 people in Vietnam and four in Thailand. The victims were believed to have caught the virus through close contact with sick poultry or their waste.

Horby’s warning yesterday came after influenza expert Klaus Stohr at the UN health agency said bird flu was “endemic” in Asia and was spreading too far and too fast to be easily contained. Malaysia was the latest country affected but the government said no human cases have emerged despite an outbreak of H5N1 in chickens near the Thai border.

Vietnam came under some criticism for declaring at the end of March that it had vanquished the virus, which re-emerged in the country in July, confirming experts’ views that it would almost certainly reappear.

Last week, the agriculture ministry said Vietnam could be on the verge of declaring itself largely safe from the bird flu virus after 10 of 11 provinces hit by bird flu had seen no new cases for 21 days up to last Thursday.

One of the visiting WHO staff in Vietnam is an epidemiologist and the other a laboratory expert. They began work this week in Hanoi by visiting hospitals that had treated suspected bird flu victims.