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Rajeev Venkayya, Special Assistant for Biodefense to U.S. President George W. Bush said "I think that number is a very optimistic number if we are talking about a 1918-wide pandemic today,"

Health experts worry that the highly pathogenic H5N1 avian influenza virus that re-emerged in Asia in 2003 and spread widely to more than 60 countries has now mutated and will spread between people, sparking a human flu pandemic.

The H5N1 virus has killed at least 300 people out of 600 known human cases and ravaged poultry stocks.

The 1918-19 "Spanish influenza" pandemic -- the worst in living history -- killed anywhere from 20 million to 100 million people. Half a million died in the United States alone. (Source : Birdflu1.net )

Last month, a Harvard University study published in The Lancet medical journal said developing countries would bear the vast majority of the 62 million deaths in a similar pandemic.

Venkayya did not give a forecast of possible deaths in a pandemic -- which the World Health Organisation and other experts say is inevitable and overdue -- but said the number of fatalities could be frightening.

"The bottom line is that they (U.S. government guesses about a toll) are all very high and all very scary," Venkayya told a meeting attended by government health and defence officials organi sed by a business chamber in New Delhi.

The U.S. government says countries need to sharply step up vaccine production capacity -- currently at around 350 million doses per year for a global population of more than 6 billion people.

Venkayya also called for urgent efforts to try to utilise adjuvants -- substances that be delivered along with vaccines and that enhance the immune response to a vaccine dose.

"So for every individual you are immunising, you can use a much smaller dose of vaccine than you would have without the adjuvant which means you can immunise many more people."

He said recent data from global drug firms such as GlaxoSmithKline Plc, which were carrying out tests on adjuvants, suggested that if they proved to be safe, they would allow countries to immunise more than 20 times more people from a single dose of vaccine.

"That is the single most promising thing on the vaccine side of the equation, I believe."

However a group of medical experts who attended a national avian flu conference last fall believe there is little chance the United States will be able to manufacture and stockpile enough vaccine or antiviral medication to stop a bird flu pandemic should the virus mutate into a form that can be spread easily from human to human, according to a survey led by researchers at Carnegie Mellon University. The results of the survey were published in the June 2006 issue of the journal Global Public Health.

The 19 medical experts who attended the Pandefense 1.0 meeting in November gave a median estimate of a less than 1 percent chance that the U.S. will have adequate stockpiles of vaccines or antiviral drugs to prevent a pandemic within the next three years. The same experts gave a median estimate of 15 percent for the probability that the avian flu virus will mutate into a strain that can spread efficiently by human-to-human contact within that time. Their median worst-case estimate of the number of people who would die, should that happen, was 6 million in the United States and 180 million worldwide. Their median best-case estimates were 500,000 dead in the United States and 20 million worldwide.

"It surprised me that they thought it was going to be this bad," said Wandi Bruine De Bruin, lead author of the study and research faculty member in the Department of Social and Decision Sciences at Carnegie Mellon.

The survey also included 17 non-medical experts from a variety of fields who were more pessimistic about the likelihood of human-to-human transmission, giving a median 60 percent chance that it would occur within three years. They did, however, have more faith in medical science, giving a median 15 percent chance of the United States having enough vaccine and a 30 percent chance that the nation would have enough antiviral medications to halt a pandemic.

"The medical experts' estimates suggest this is a bigger risk than anything else we are facing," said Baruch Fischhoff, a study co-author and the Howard Heinz University Professor of Social and Decision Sciences and Engineering and Public Policy at Carnegie Mellon.

Both the medical and the non-medical experts agreed that the greatest hope for mitigating the effects of an avian flu outbreak among humans lies in heightened global surveillance and, should the virus become pandemic, hand washing, mask wearing and social distancing. Unfortunately, the efficacy of such strategies in preventing the spread of infectious diseases has not been extensively studied, Bruine de Bruin said. Although the federal government has expressed a commitment to open communication about these risks, its messages have not yet been scientifically evaluated, according to Fischhoff.