Federal officials contracted with two companies -- Chiron Corp. and Sanofi Pasteur -- for those doses, and most already have been produced, said Bill Hall, a spokesman for Health and Human Services (HHS).
The second vaccine must be developed and tested, and HHS had no estimate for the cost of that work.
Margaret Chan, who is spearheading the WHO efforts against the virus, said it poses a greater challenge to the world than any previous infectious disease.
Poland on Monday confirmed its first outbreak of the disease, saying laboratory tests found that two wild swans died of the lethal strain.
Several cats have also tested positive for the deadly strain in Austria's first reported case of the disease spreading to an animal other than a bird, officials in that country said on Monday.
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