The first vaccine doses for the H1N1 influenza, or swine flu, will be available in the form of a nasal spray, the US Centres for Disease Control and Prevention (CDC) has said.
About 3.4 million doses of the nasal spray vaccine - which can be used only by those between the ages of 2 and 49 - will be ready for distribution to 90,000 providers by the first week of October, epidemiologist Jay Butler, chief of the CDC's 2009 H1N1 vaccine task force, said on Friday.
"The government has purchased 195 million doses. It's a very large logistical undertaking," Butler said. "You have to get this vaccine from five manufacturers out to some 90,000 provider sites around the country."
He said it was also likely that injectable vaccine shots would be available by early October. The CDC said it estimated that 20 million vaccine doses a week would be delivered by the end of October.
President Barack Obama said on Thursday that the United States will share 10 per cent of its H1N1 vaccine supply with other countries to combat the global spread of the pandemic.
The US vaccines would be made available to countries through the World Health Organisation (WHO), and on a rolling basis in cooperation with Australia, Brazil, France, Italy, New Zealand, Norway, Switzerland and Britain.
According to the latest WHO estimates, more than 277,607 people worldwide have been sickened by swine flu this year, with at least 3,205 reported deaths.
CDC officials confirmed on Friday that swine flu was reported in all 50 US states, with 21 states reporting widespread flu activity.
"We don't see that kind of activity this time of year usually," said Daniel Jernigan, deputy director of the CDC's influenza division. "It's a very strange thing for us to see that amount of influenza at this time of year."
Each year during the regular flu season, an estimated 36,000 people die in the US alone, and at least 200,000 are hospitalised.