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New Zealand is among nine well-off countries who have agreed to share extra swine flu vaccine with less-developed countries.
The United States today pledged 10 percent of its vaccine supply, joining Australia, Brazil, France, Italy, New Zealand, Norway, Switzerland, and Britain.
The World Health Organisation (WHO) has been working to persuade well-off countries to share their supplies of vaccine.
"They own most of the vaccine out there," WHO's Dr Keiji Fukuda told scientists at an Institute of Medicine pandemic influenza meeting this week.
"The single biggest (issue) we have to deal with is disparity."
Foreign Affairs Minister Murray McCully was "fully-supportive" of the scheme.
"Pandemics such as the H1N1 (swine) flu virus require a global response because they know no borders, so the initiative announced by (US President Barack Obama) today is very welcome."
New Zealand will spend $7.1 million helping Pacific nations prepare for a possible pandemic.
If the Government goes ahead with a pandemic immunisation campaign in New Zealand, supplies will also be provided to the Cook Islands, Tokelau and Niue, Mr McCully said.
Vaccine makers GlaxoSmithKline and Sanofi-Pasteur previously pledged 120 million doses to WHO. Experts estimated 80 percent of the world's nearly seven billion people lived in the developing world, with little hope of getting a vaccine.
WHO has been urging countries that pre-ordered vaccine from the 25 or so manufacturers to share some of it.
"Whatever is available to WHO will be made available first to least-developed countries, about 49 countries, with the intention of providing them to vaccinate their healthcare workers," Fukuda said.
The United States has ordered 195 million doses of H1N1 vaccine from five makers - Glaxo, Sanofi, Australia's CSL, AstraZeneca's MedImmune unit and Novartis.
This is not enough to cover 300 million people but the US Centres for Disease Control and Prevention says almost every year influenza vaccines go unused and millions of doses are thrown away.
Countries all expect a bonus with the news that many of the vaccines being made will protect people with a single dose.
Most had ordered vaccine with the expectation that two doses would be needed, so the many now have more than anticipated.
"We will have enough vaccine for every American who wants it," White House spokesman Reid Cherlin said.
European countries agreed to share vaccine this week under a European Commission plan.