Antivirals, used intensively in an area where a pandemic is emerging and combined with other measures such as quarantine and isolation, could help delay the spread of a virus, according to the World Health Organization.

The antiviral oseltamivir, known commercially as Tamiflu, is the only treatment proven to be effective in humans against bird flu. WHO would use the reserve stock of the drug to respond quickly to any emerging influenza pandemic if stocks held by national governments were not enough.

"If a flu pandemic were to emerge, these drugs could be flown quickly to the center of a potential pandemic," said WHO chief Dr. Lee Jong-wook. "We urge other countries to help us build up the international stockpile."

Tamiflu could help reduce illness and death and could potentially contain an emerging pandemic virus or slow its spread when combined with other measures, WHO said.

Timing and Severity Is Uncertain

The health agency is currently monitoring bird flu outbreaks in parts of Asia, Russia and Kazakhstan and has warned that it could evolve into a global influenza pandemic if the virus mutates into a form that can transmit easily between people.

The longer the H5N1 bird flu strain circulates, the greater the risk that the virus will mutate into a form that can be spread between people and trigger a pandemic, WHO said. If that happens, slowing the pandemic's spread would critical to allowing medical authorities time to produce vaccines against the virus and introduce other emergency measures.

Antivirals, used intensively in an area where a pandemic is emerging and combined with other measures such as quarantine and isolation, could help delay the spread of a virus, according to the health agency.

3 Million Treatment Courses

WHO said Roche will keep 3 million treatment courses, or 30 million capsules, in reserve for up to five years. The first million treatment courses will be ready early next year, with the remaining 2 million ready before mid-2006.

WHO is urging countries to step up preparations as experts predict an influenza pandemic will occur, although the timing and severity is uncertain.