Washington  - The A-H1N1 virus, or swine flu, could infect nearly half the population in the United States and kill between 30,000 to 90,000 people this autumn and winter, according to a projection from President Barack Obama's scientific advisers.

Between 20-40 per cent of the population, or 60-120 million people, could display flu symptoms, the panel said. A swine flu epidemic could lead to as many as 1.8 million hospital admissions, placing enormous stress on the already strapped health care system, the report from the president's Council of Advisers on Science and Technology said Monday.

These projections were developed from models put together for "planning purposes only," cautioned Tom Skinner, spokesman for the US Centres for Disease Control and Prevention (CDC) on Tuesday.

"At the end of the day we simply don't know what this upcoming flu season is going to look like," Skinner was quoted as saying by Bloomberg News. "It could be be severe, it could be mild, we just don't know."

So far, there have been 522 swine flu-related deaths in the US, with 7,983 hospitalizations, the CDC said.

Last week, the World Health Organization reported that 1,799 people have died of swine flu since April, and that 182,166 infections had been confirmed by national health authorities.

The Americas remained hardest hit, with at least 105,882 infections and 1,579 deaths, WHO said.

US health experts have said that because the 2009 swine flu virus - which first emerged in Mexico in April - is a new strain, it's likely to infect more people than usual who have no immunity to it.

A swine flu resurgence in the US could begin as early as September, peaking in October. A vaccine is currently projected to become available only mid-October and it will take several weeks for people to develop immunity.

An estimated 30,000-40,000 people die from seasonal flu each year in the US, the council's report said. The additional deaths projected from swine flu would most likely be concentrated among children and young adults.

The report said that the 2009 swine flu virus has not so far shown the virulence associated with the pandemic of 1918, which is believed to have killed between 40-100 million people worldwide.

Science now has tools to mitigate a potent flu epidemic, but the 2009 virus remains a "serious threat to our nation and the world," it said.

The experiences from the 1918 pandemic have over the years helped the government shape preparation for influenza epidemics. While there is cause for concern, experts also point to the swine flu "fiasco" of 1976, when 45 million Americans were vaccinated for a virus that never spread beyond a tiny cluster.

Some health experts said the council's projections had been blown out of proportion. "Influenza, you can make all the predictions you want, but it's more difficult than predicting weather," Peter Gross, chief medical officer at Hackensack University Medical Centre in New Jersey told Bloomberg. (dpa)