Signs that the H5N1 bird flu virus may be developing resistance to frontline drug Tamiflu in some patients are not necessarily a cause for alarm, a senior World Health Organization official said in Geneva Thursday.

Keiji Fukuda, a scientist at the WHO's global influenza programme, said some resistance was inevitable with any kind of drug.

"Whenever you use any kind of drugs, antivirals or antibiotics, you expect to see resistance develop in organs. Finding some resistance in and of itself is not surprising and is not necessarily alarming," he said.

But findings published in the New England Journal of Medicine that four of eight patients treated in Viet Nam for bird flu infections had died despite the use of Tamiflu indicated that more research was needed into how best to use the drug, Fukuda said.

"It just points out the need for more information... What really is critical is understanding whether the way we are using the drugs contributes to that (resistance)," he added.

Tamiflu, made by Swiss firm Roche, remained an "excellent choice" among a limited number of antivirals available against the deadly virus, the WHO official said.

Shanghai Pharmaceutical Group last month became the first in Asia to secure a licence from Roche to produce a generic variety of Tamiflu.

Tamiflu losing effect over H5N1, researcher

Tamiflu is losing its effect over H5N1 virus as two patients showed resistance to this famous anti-bird flu drug, researchers say.

In a report completed in the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam, Menno D. de Jong, clinical medicine expert from Oxford, together with his colleagues pointed out that bird flu virus is subject to very fast variation, and four of eight N5N1-infected patients died here in spite of antiviral treatment by taking Tamiflu. Drug resistance has been found in the body of two patients. Just like against the AIDS, "cocktail" therapy is also needed in fighting bird flu, using more than one kind of medicine, the researcher said.

Two more human deaths from bird flu in Indonesia were confirmed yesterday, bringing the known global total to 73, while cases including survivors would rise to 141. All the deaths so far have been in Asia.

The H5N1 strain of bird flu has also killed hundreds of millions of chickens and ducks since it started ravaging poultry stocks across Asia in 2003.

The WHO confirmed that a 39-year-old man and an 8-year-old boy died earlier this month of bird flu, raising Indonesia's toll to 11.