By Laura MacInnis GENEVA, Oct 23 (Reuters) - Scientific advances have dramatically increased the supply of life-saving flu vaccine that could be used to fight a global pandemic, the World Health Organisation (WHO) said on Tuesday.

Marie-Paule Kieny, director of the WHO's initiative for vaccine research, said a more efficient formula had allowed drug makers to make far more flu vaccines than previously thought possible.

The United Nations health agency warned last year that only 100 million courses of pandemic vaccine could be produced immediately, but she said it was now likely that 4.5 billion could be made each year by 2010.

"We are beginning to be in a much better position," Kieny told journalists in Geneva, where pandemic influenza experts met last week to review progress in vaccine production and supply.

Following scientific advances, drug makers such as Novartis <NOVN.VX>, GlaxoSmithKline <GSK.L> and Sanofi Pasteur <SASY.PA> were now able to produce 565 million doses of seasonal flu vaccines a year, Kieny said, versus only 350 million in 2006.

By 2010, pharmaceutical companies would be able to create 1 billion doses of seasonal vaccines per year, she said.

Because seasonal vaccines provide immunity against three strains of virus and pandemic shots only one, many more doses of the anti-bird flu jabs could be produced in the same facilities.

Health experts almost universally agree the world is overdue for an influenza pandemic. Such global epidemics strike three times in a century, on average, when a new strain of flu emerges that humans have no immunity against.

While nobody knows for certain which strain will trigger it, the main suspect is the H5N1 bird flu virus that has killed 203 people in 11 countries since 2003. About 60 percent of those infected have died from the virus, although it has not yet mutated into a form that passes easily between humans.

Kieny stressed that much more needed to be done to reach the goal of having enough vaccine to serve the world's 6.7 billion people in the event of a pandemic, which could occur in several waves around the globe.

A report from a WHO pandemic flu advisory group estimated $3 billion - $10 billion in investments would be required to reduce gaps between potential vaccine demand and supply in a pandemic.

That group, which met in Geneva on Friday, concluded governments should support seasonal flu immunisation programmes to encourage drug makers to keep making more of the vaccines.

Seasonal flu causes severe illness in 3 to 5 million people every year, in addition to 250,000-500,000 deaths, mainly among the elderly and chronically ill.

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