Vaccines are the most powerful public health tool for control of influenza, and the U.S. government is working closely with manufacturers to take steps in the process to manufacture a novel H1N1 vaccine. Working together with scientists in the public and private sector, CDC has isolated the new H1N1 virus and modified the virus so that it can be used to make hundreds of millions of doses of vaccine. Vaccine manufacturers are now using these materials to begin vaccine production. Making vaccine is a multi-step process which takes several months to complete.  Candidate vaccines will be tested in clinical trials over the few months. 

Source: CDC H1N1 Flu | H1N1 Flu and You