Jason Kottke has a great post on how the H1N1 vaccine is made.
The most striking feature of the H1N1 flu vaccine manufacturing process is the 1,200,000,000 chicken eggs required to make the 3 billion doses of vaccine that may be required worldwide. There are entire chicken farms in the US and around the world dedicated to producing eggs for the purpose of incubating influenza viruses for use in vaccines. No wonder it takes six months from start to finish. But we’ll get to that in a minute.
Of course as complicated as it is to find 1,200,000,000 eggs to make the vaccine, those eggs don’t work nearly as well as they had hoped.
Side note. You may have noticed that the H1N1 vaccine has been difficult to find in some places around the US. The vaccine manufacturers have said that the Pandemic H1N1/09 virus when combined with the standard laboratory virus does not grow as fast in the eggs as they anticipated. The batches of antigens from each egg have been smaller than expected, up to five or even ten times smaller in some cases. Hence the slow rollout of the vaccine.