The world is far from being fully prepared for a flu pandemic, a leading US infectious diseases expert said on Saturday, warning there were big gaps in surveillance and basic knowledge.

Experts have long warned that the H5N1 bird flu virus could trigger the next pandemic and kill millions of people if it becomes easily transmissible among humans.

"We are a long way from being fully prepared. We do not have a vaccine that will provide universal protection. We don't have surveillance in every country. We don't have control of the virus in animal reservoirs," said Julie Gerberding, director of the US Centers for Disease Control and Prevention.

"We have huge gaps in our basic understanding of influenza and what will be the trigger that allows it to move onto its next host and potentially become more transmissible to humans," she told a news conference in Kuala Lumpur on the sidelines of an infectious diseases conference.

H5N1 remains essentially a disease among birds. But while it has infected only 385 people around the world since late 2003, it has killed 243 of them, World Health Organisation (WHO) figures show.

Humans have no natural immunity against it and any pandemic caused by this virus is widely expected to be catastrophic.

Sharing samples

Indonesia has the highest human casualties from H5N1, and the disease is now endemic in most parts of the country. The virus has infected 135 there since late 2003, killing 110.

But Jakarta's reluctance to share virus samples has caused deep concern among experts.

Indonesia said earlier this month it was changing its policy on reporting human cases and would announce the death toll every six months instead of on a case-by-case basis.

However, the Indonesian Health Ministry has reported two deaths from bird flu in recent weeks to the WHO, easing concerns about how much information it would share.

"Our preparedness is only as strong as its weakest link. It's imperative that every nation does its part to conduct its own surveillance and preparations and allow information to be shared in compliance with the WHO and international health regulations," Gerberding said.

"We can't afford to have this virus move in human populations undetected and unreported. International health regulations do require nations to report documented cases of avian influenza in a prompt manner and we hope all countries will be compliant with this request," she said.

Sharing of virus samples is important because experts can run tests to see if there are mutations in the virus, such as whether it may have become more transmissible among people and whether it may have become resistant to certain drugs.

Such analyses will also track footprints of the virus, showing where it may have spread, so that measures can be taken to stop its geographical proliferation.

International health regulations require the 193 member states of the WHO, a United Nations agency, to report human cases of bird flu within 24 hours.

Indonesia is reluctant to share virus samples because it says it is unfair for foreign companies and agents to use them to make vaccines without giving assurances that the country would get access to the drugs.