US health officials have confirmed that the entire stock of flu vaccine from a British producer is unusable.
The US has lost almost half its annual supply of vaccine
The US had hoped to salvage some of the doses made by Chiron, which account for nearly half of its annual supply. But tests have shown contamination.
Officials have been trying to arrange deliveries from other nations, such as Canada - but say it will be hard to get regulators to approve them by winter.
Long queues for the vaccine have formed at pharmacies in parts of the US.
An elderly woman collapsed and died while queuing for hours for an injection in the state of California.
US Health Secretary Tommy Thompson on Thursday urged local officials to investigate reports from several states about companies raising prices to exploit the vaccine shortage.
The US Food and Drug Administration (FDA) says the problem with the British stock is a bacteria, serratia, which can cause blood poisoning and infections of the urinary and respiratory tracts.
The administration also found serious
manufacturing problems cited by British regulators.
"We believe all of the lots produced by that plant are
suspect at this point," FDA Acting Commissioner Lester Crawford said.
cannot allow them to be used."
The comments came as FDA scientists finished a
week-long stint at the factory where Chiron had made about 48 million doses of the vaccine originally destined for US use.
Last week the UK Department of Health suspended Chiron's licence for at least three months.
The decision followed an announcement by the company in August that millions of Fluvirin vaccines had been contaminated, although it subsequently said its products were back up to standard.
Fluvirin is the second most widely used flu vaccine in the US.