By Michelle Roberts
BBC News health reporter
Experts say it is no longer a case of if but when a pandemic of bird flu hits the human population.
Some countries have already started stockpiling drugs and testing vaccines to beat the virus.
The UK government had been criticised for being slow on the uptake, but announced its full pandemic plan in March this year.
The World Health Organization (WHO) recently urged all countries to develop or update their influenza "pandemic preparedness plans" after experts estimated anywhere between two and 50 million people could die if a pandemic hits and the world is not prepared.
Good health care will play a central role in reducing the impact, yet the pandemic itself could disrupt the supply of essential medicines and health care workers could fall ill.
Even in the best-case scenario, two million to seven million people would die and tens of millions would require medical attention, WHO says.
Experts have used their knowledge about past pandemics, such as the 1918 Spanish flu outbreak, and their experience with the strain of bird flu that has killed 57 people in Asia since 1997, to make a prototype vaccine.
If this strain, called H5N1 and which spreads from birds to humans, mutates to spread easily between humans, scientists believe this vaccine should help beat a pandemic.
However, a different strain might mutate to cause a pandemic and it would take many months to produce a vaccine after a pandemic had started.
By having stocks of the prototype, scientists will be able to learn how to work with this material, which is new to the industry, which, in turn, should help speed the production of a vaccine to use in a pandemic.
Countries will also be able to test things such as the optimal dose of vaccine required and manufacturing capacity.
While this is happening, antiviral drugs can be used to help contain the initial outbreak of a pandemic.
RECIPE FOR A PANDEMIC
A novel virus to which the community has no or little immunity
A virus that can replicate in humans and cause serious illness
A virus that can be passed efficiently from human to human
US, French and Italian governments have heeded WHO's advice and all have placed orders for the vaccine. As yet, the UK has not.
A spokeswoman from the Department of Health said its plan for a potential pandemic had taken on board the latest advice, technology and medicine.
"The department does not believe stockpiling vaccines is the best course to follow, as we cannot be sure what mutation of the virus would be involved in any pandemic."
Window of opportunity
Professor John Oxford, a virologist at Queen Mary's School of Medicine, said this was disappointing and could leave the UK vulnerable.
"There is a window of opportunity here now where we can begin to prepare ourselves," he said.
"But that window will close over coming weeks and months, so the sooner we act the better.
"The big time bomb here is that once there is 100% evidence of human to human spread it will be too late to do anything about it. Once it starts it's likely to move quickly.
"We have to make up our minds now before it arrives on our doorstep."
Professor Oxford warned that once vaccine and antiviral drugs were ordered, it would take several months for the supplies to be made and delivered.
He said Canada and Australia had already ordered enough to protect a quarter of their populations.
He believes other countries should do the same and that richer nations should buy extra to donate to poorer countries.
"By ring-fencing an early outbreak there, we can help protect ourselves here," he said.
Professor Albert Osterhaus, professor of virology at Erasmus University Hospital, in Rotterdam, said most European countries were relatively unprepared.
"National plans have been established but a lot of gaps have got to be filled in," he said.
"As well as drugs and vaccines, there are other things that are logistic, like hospital capacity."
In the event of an outbreak, patients would need to be isolated to prevent them infecting other people and close contacts, such as close family members and hospital staff, might need treatment.
He said it would be helpful to have a pan-European policy rather than each country working on its own.
But Dr Alan Hay, director of the World Influenza Centre in London, said: "I would not say we have been dragging our heels.
"To say that one country is more prepared than another is to assume that one can be very well prepared.
"If a pandemic strikes without warning then really there is only a certain amount one can do to combat the impact.
"We do not know what the scenario we might face is. It might be like Sars where it can be contained at the early stage."
Should early containment fail, once a certain level of efficient transmission is reached, no interventions are expected to halt international transmission, according to WHO.
The priority would then shift to minimising deaths and illness.
During pandemics, more severe disease tends to arrive with the second wave, it says.
Should this happen, a few more months might be available at the beginning of an outbreak to make more vaccine.
Each day gained could mean an additional five million doses of vaccine, WHO estimates.