Because H1N1 is an exotic virus that we have no natural immunity to, we may need 2 vaccines

TIME: It will take longer to manufacture H1N1/09 vaccine — and since very few people have immunity to this flu strain, people may need two shots, which means annual global capacity would drop to a little more than 400 million doses.

SHOOT: 400 million doses for 7 billion people. That's 1 dose for every 17.5 people.
Adjuvant vaccines could be used, but that's relatively new territory.

TIME: adjuvants — chemicals added to a vaccine that boost the immune system's response.
The U.S. has never licensed an adjuvated flu vaccine, which could delay approval in America. And while Europe doesn't have that problem, if Washington demands pure vaccine from its suppliers, that would impact supply for the rest of the world. For now, adjuvants are seen in the U.S. as a last resort.

clipped from www.time.com Italian students arrive at England's Standsted Airport wearing masks to protect against swine flu. "We don't know if it will actually ever completely go away," said David Butler Jones, the public health chief of Canada, which has been unusually hard hit. "We're still seeing new cases, so nobody should let down their guard." The real test will come in the fall, however, when the Northern Hemisphere's flu season returns with a vengeance. (Southern Hemisphere nations are currently in the early weeks of their flu season, and H1N1/09 has caused real trouble in Argentina, which has more than 130 confirmed deaths — second only to the U.S.) There is always a chance that the virus could become more virulent when it returns in the fall — just as the deadly 1918 pandemic did. Key to the world's defense against the flu will be an effective vaccine, and vaccine companies have been gearing up to produce hundreds of millions of doses. But vaccine makers have already reported problems;