Scientists have renewed their warnings about the potential global effect of a flu pandemic on health and economy.
Humans contract avian flu through close contact with birds
Experts estimate a fifth of the world's population could be affected, with 30m needing hospital treatment and around 7.5m dying.
Writing in Nature, they warn the world's economy could also be damaged by effects on international trade as well the effect of death and illness.
The US and Dutch experts call for a unified approach to the problem.
They say only a global effort, rather than separate work by individual countries, will mean any pandemic can be contained.
Fears of a pandemic have arisen because of outbreaks of the H5N1 bird flu strain in south east Asia, which has caused a total of 53 confirmed human deaths, according to the World Health Organization.
It is estimated that up to 60% of humans infected by the virus have died.
There are indications that it can spread between humans, although so far not in the feared mutated form which could fuel a pandemic.
A case in Thailand indicated the probable transmission of the virus from a girl who had the disease to her mother, who also died.
The fear is that if the H5N1 virus did mutate and spread amongst humans, it would do so rapidly and affect millions.
Experts repeatedly warn such a pandemic would be far worse than the one which occurred in 1918, which killed between 20 and 40 million people.
Scientists are working to develop a vaccine against bird flu, but are hampered by not knowing what form it would take, should it spread amongst humans.
In addition some countries, including the UK, have announced plans to stockpile millions of doses of anti-retroviral drugs which could be used to treat people during a pandemic.
Writing in Nature, a team from the Dutch Erasmus Medical Centre led by Dr Albert Osterhaus, said there was currently a lack of coherence in how countries tested for avian flu in people, and in how the effects of the disease were monitored.
The scientists also called for better surveillance of bird populations to assess which strain of bird flu they are carrying.
They write: "To limit the effects of flu on public health and livestock production, integrated and effective action from all the disciplines involved is urgently needed, rather than ad-hoc responses at a national level.
They called for a global task force, including human and animal health experts, as well as health policy advisors to be set up under the auspices of the WHO.
And Professor Michael Osterholm, from the Centre for Infectious Disease Research and Policy at the University of Minnesota in Minneapolis, US, writing in the same journal, said: "The arrival of pandemic flu will trigger a reaction that will change the world overnight.
"There will be an immediate response from leaders to stop the virus entering their countries by greatly reducing and even ending foreign travel and trade - as was seen in parts of Asia in response to the severe acute respiratory syndrome (Sars) epidemic.
He added: "These efforts are doomed to fail given the infectiousness of the virus and the volume of illegal crossings that occur at most borders. But government officials will feel compelled to do something to demonstrate leadership.
"Individual communities will also want to bar 'outsiders'. Global, national and regional economies will come to an abrupt halt."
He added: "Unfortunately, most industrial countries are looking at the vaccine issue through myopic lenses."
Professor Osterholm warned: "National, regional or local plans based on general statements of intent or action will be meaningless in the face of a pandemic."