GENEVA - Vaccine makers could produce 4.9 billion pandemic flu shots per year in the best-case scenario, the head of the World Health Organization said on Tuesday, as rich and poor countries grappled over limited supplies.

WHO Director-General Margaret Chan told reporters after her meeting with 30 pharmaceutical companies that there are a lot of unanswered questions about how many vaccines could be made to protect vulnerable people from the new H1N1 virus.

That is a very optimistic maximum capacity, she said of the 4.9 billion estimate, which would be significantly lower if people need more than one injection to gain immunity against the strain or if seasonal flu vaccine-making continues.

Bringing a new pandemic vaccine to market -- if it goes ahead -- is expected to take 4-6 months, according to the WHO. It must be tested first on ferrets and then on humans in clinical trials before regulatory authorities can approve it.

U.N. Secretary-General Ban Ki-moon told the news briefing that while the newly-discovered virus strain now appears mild, it needs to be closely watched as it spreads around the world and starts to afflict impoverished countries.

We may be in a grace period with H1N1 but we are still in the danger zone, Ban said.

Earlier on Tuesday, the United Nations chief said it was essential for drugmakers to work with governments to avert the worst potential impacts of the flu, which has killed 79 people and infected nearly 10,000.

Partnerships with the private sector are absolutely vital, he told representatives of the WHO's 193 member governments gathered in Geneva, urging them to think beyond their borders in their response to the H1N1 strain.

Though most people infected so far have experienced mild symptoms similar to the common flu, pregnant women and people with HIV/AIDS, diabetes and other health problems appear to be vulnerable to more severe effects like pneumonia.

Health experts have said weather could affect the continued spread of the virus, with more cases expected as countries in the southern hemisphere move into winter. Flu viruses typically thrive in cold and dry environments.

READY TO PRODUCE

Pharmaceutical executives taking part in Tuesday's vaccines meeting at the WHO's Geneva headquarters said they were primed to ramp up production of H1N1 vaccines if needed, and would await more directions about how to balance their output.

Our companies stand ready to produce H1N1 vaccines when the recommendation comes from the WHO, the International Federation of Pharmaceutical Manufacturers and Associations said.

Six companies have pledged to make 10 percent of the vaccine they produce available for distribution to poor countries, and eight are in talks about donations, said Gelmer Leibbrandt, general manager of Schering-Plough's Nobilon.

Chan said that vaccine makers have shown a very serious commitment to help the international community prepare for a pandemic of flu, which could be mild in its effects to start and become more severe as it circles the globe.

Questions remain about whether an H1N1-only vaccine is needed in the near-term -- especially if its production cuts the world's supply of injections for seasonal flu, which kills up to 500,000 people a year and causes severe illness in millions.

U.S. Health and Human Services Secretary Kathleen Sebelius said pharmaceutical companies should ramp up their production of seasonal flu shots and then later switch to pandemic injection making if that is necessary.

There is still so much uncertainty about this virus that it is really premature for us to even make a determination about how many people would appropriately be vaccinated, in what order, how many doses will be required, at what point. All those discussions are still very much underway, Sebelius said.

Ban, in his remarks to the World Health Assembly, called on wealthy nations to help support poorer states fight the flu.

But one international official said he expected battles ahead as governments try to secure finite supplies of antiviral drugs and vaccines to protect their populations.

Enabling poor countries to be able to access the various medical supplies they need is going to be a critical political and technical issue, he said. This issue will require political attention.

The WHO has said the world is on the brink of pandemic from the H1N1 virus, which has been most prevalent in North America and begun to infect large numbers in Japan, Britain and Spain.

Medicine