By Laura MacInnis

GENEVA, Aug 6 (Reuters) - Indonesia has yet to provide usable samples of the H5N1 bird flu virus to the World Health Organisation, compromising international efforts to prepare for a pandemic, a top WHO official said on Monday.

David Heymann, assistant director-general for communicable diseases at the U.N. agency, said the three specimens Jakarta sent in May, which came from two humans infected with the deadly influenza strain, contained fragments but no live virus.

Indonesia is now the only country that has not shared samples of H5N1 that drugmakers can use to develop vaccines. Heymann said this raised global pandemic risks, given that vaccines now being developed cannot protect against the virus mutations that proved lethal there.

"Indonesia is aware of these issues and is working with WHO ... to see how they can best begin sharing again," he said. "We are hoping that that will begin fairly soon."

Indonesia has had 81 confirmed human deaths from bird flu, more than any other country. The disease is endemic among birds in most parts of Indonesia, where millions of backyard chickens are kept close to humans.

Although most people who have caught bird flu have had direct or indirect contact with infected fowl, experts fear the constantly-mutating virus could change into a form easily transmitted from person to person and sweep the world.

Jakarta, which has complained poor nations would not be able to afford vaccines being developed, earlier this year refused to share virus samples with the WHO unless it had guarantees they would not be used commercially.

While it later agreed to ship specimens under a deal with the Geneva-based agency meant to improve access to vaccines, Heymann said Indonesia had not shared any virus samples since the three unusable ones were shipped in May.

China last sent bird flu samples in June. Vietnam has been trying to share specimens but is currently wrestling with shipping regulations, both in Vietnam and abroad, he said. H5N1 vaccines developed from live virus samples could be used to contain an early epidemic among humans or could be used to prime certain populations for a possible outbreak to give them a certain amount of immunity, Heymann said.

Influenza vaccines have to be reformulated every year to match the circulating strains because the virus mutates often.

Health experts met in Singapore last week to discuss how influenza viruses should be shared, a debate that is expected to continue until the World Health Assembly in May 2008 when the WHO's 193 member states formally take up the issue.

According to WHO figures, 319 people have become infected with bird flu since 2003 and 192 have died.

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