Companies could potentially turn out 4.9 billion doses of vaccine against the new H1N1 influenza strain within a year under the best-case scenario, World Health Organization officials said on Tuesday.

WHO director-general Dr Margaret Chan told reporters after a meeting with 30 pharmaceutical companies that WHO was working to secure supplies of vaccine for poor countries in case of a pandemic.

US health officials said they were finding higher-than-expected numbers of cases of seasonal influenza still circulating and worried that a drug-resistant strain may mix with the new H1N1 swine flu strain to create a dangerous new strain.

United Nations secretary-general Ban Ki-moon said it was essential for drugmakers to work with governments to avert the worst potential impacts of the new H1N1 strain, which has killed 81 people and been confirmed in nearly 10,000 globally.

"Partnerships with the private sector are absolutely vital," Ban 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.

Six companies have pledged to make 10 per cent 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 vaccine unit Nobilon.

Chan said that vaccine makers have shown a very serious commitment to help the international community prepare for a pandemic of flu, which, while seemingly mild so far, could become more severe as it circles the globe.

Vaccine questions

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

US Health and Human Services Secretary Kathleen Sebelius said pharmaceutical companies should ramp up their production of seasonal flu vaccine and then later switch to pandemic injection making if 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 under way," Sebelius said.

WHO said companies plan to produce approximately 480 million doses of seasonal vaccine in 2009 -- each one containing three separate vaccines against the three most common circulating flu strains.

The agency said 430 million doses would be available by July 31.

"For influenza A (H1N1), it is estimated that up to 4.9 billion doses could be produced over a 12-month period after the initiation of full-scale production," WHO said in a statement. That assumes it is as easy to make a vaccine against the new H1N1 virus as it is for seasonal flu, and that the vaccine could be stretched out to the maximum.

"In this situation, there is a potential access for the UN of supplies of up to 400 million doses," WHO said.

In Mexico, the Health Ministry updated the death toll to 74 on Tuesday as confirmations came in that people who died were in fact infected with the swine flu strain. It said confirmed swine flu cases now total 3,734.

The US Centers for Disease Control and Prevention said there have been 5,469 confirmed cases of the new flu and has said this is only the tip of the iceberg. CDC acting director Dr. Richard Besser estimated last week there were 100,000 cases.

Officials in St. Louis County, Missouri, reported a seventh US death from the new flu on Tuesday, a 44-year-old man.

Strain mixing

The CDC's Dr. Anne Schuchat said she was worried the new strain may mix with seasonal flu strains, which are still circulating.

The seasonal H1N1 strain is now resis