The Food and Drug Administration yesterday again denied the agency had any early indications that there were serious problems at a British vaccine company that was supposed to supply half of the U.S. flu vaccine.

Lester M. Crawford, the FDA's acting commissioner, made the statement during a telephone briefing in response to reports that the agency had been alerted before last week that Chiron Corp.'s flu vaccine plant in England was experiencing major difficulties. On Friday, British health officials said U.S. officials were informed Sept. 13 that problems at Chiron's plant could disrupt supplies.

Crawford denied that was the case. Although the FDA was in regular contact with Chiron and British health officials, he said, the agency was not alerted to any serious concerns until last week, when British officials abruptly announced they were shutting down the plant.

"I want to refute as strongly as possible the contention . . . that FDA knew before October 5 that there was evidence of a problem serious enough for [British officials] to suspend Chiron's license to distribute or export influenza vaccine for the upcoming flu season," Crawford said.

The Chiron shutdown has thrown U.S. preparations for the upcoming flu season into turmoil. U.S. officials had been expecting Chiron to supply about 48 million doses of vaccine. The British officials took the action because some of the vaccine had been contaminated by bacteria.

The surprise decision has forced U.S. officials to recommend that healthy adults forgo the vaccine this year so the remaining supplies can be used for those at highest risk -- primarily babies, the elderly and people with weak immune systems.

Crawford said the FDA had been aware that some contamination had occurred at the plant during early stages of vaccine production in 2003, but that issue was subsequently resolved. The agency then learned in August that another contamination problem had been detected at the plant, but believed it was limited to just eight lots of vaccine and would not endanger the majority of the plant's production.

"Neither of our most recent inspections gave any indication that Chiron would not be able to fulfill their recent public promise to deliver between 46 and 48 million . . . doses to the U.S. market beginning in early October," Crawford said.

The British government apparently decided it could not alert the United States or any other countries about the impending shutdown because of legal constraints on what officials could say publicly before officially announcing the action, Crawford added.

"We do not have a data-sharing agreement . . . that would tend to force them to inform us of this kind of thing," Crawford said.