U.S. and British drug regulators met on Thursday to discuss the closing of a flu-vaccine plant in northern England that has triggered an international vaccine shortage - but there was no immediate resolution of the crisis.

Britain’s Medicines and Healthcare Products Regulatory Agency (MHRA) revoked Chiron Corp’s flu vaccine licence earlier this week because of bacterial contamination at the plant in Liverpool.

Now U.S. officials are trying to find out if all 48 million doses from the factory destined for the United States this year will be kept off the market.

A spokeswoman for the MHRA declined to divulge details of the talks between MHRA officials and a visiting team of experts from the U.S. Food and Drug Administration (FDA) but said the blanket ban remained in place for now.

“The suspension of their licence means they (Chiron) cannot supply this vaccine to any market anywhere in the world. That may change after discussions, but that is the position at the moment,” she said.

The FDA experts will visit the Liverpool plant on Saturday and Sunday, accompanied by MHRA staff, to see the problems for themselves.

Chiron was one of only two major manufacturers of flu vaccine to the United States, and the loss of an entire year’s production has left the U.S. scrambling for extra supplies.

The Liverpool factory, which Chiron acquired when it bought British biotech firm PowderJect Pharmaceuticals in 2003, was expected to supply nearly half of U.S. flu vaccines for the 2004-2005 season just starting now.

Since influenza vaccine takes months to manufacture and has to be made fresh every year based on circulating strains, it is likely to prove difficult to find alternative supplies.

The shutdown is less a problem in Britain itself since the Chiron plant only accounts for 10-20 percent of supply.

MHRA officials also met with Chiron executives on Wednesday to discuss action needed to bring the Liverpool site up to standard.

“It was fairly constructive and the company accepted MHRA’s findings. MHRA will offer support and advice to Chiron about how they might make the improvements so that they can resume their manufacture of the Fluvirin vaccine,” the spokeswoman said.