Normally, the company would not see any results until all patients had been followed for the entire length of the trial, but Tularik will take a look at a small percentage of these patients while the clinical trials are still ongoing in order to make sure that there are no unexpected problems with the drug's safety or efficacy.

FORBES: Magazine Article

The Department of Health also holds a strategic reserve of about 400, 000 doses as an "insurance policy" in case there are problems with supply and manufacturers have no vaccine supplies available to order.

BBC: Flu vaccine 'withheld for safety'