British regulators gave the go-ahead Wednesday for Chiron Corp. (search) to resume production of flu vaccine, ending a five-month suspension that caused widespread shortages in the United States. The announcement sent Chiron's stock soaring almost 10 percent.

In October, Britain's Medicines and Healthcare Products Regulatory Agency (search) (MHRA) barred the Emeryville, California-based company from shipping to the United States some 48 million doses of its Fluvirin-branded flue medicine made in its Liverpool, England factory because of contamination concerns.

Chiron had been expected to supply nearly half the U.S. vaccine supply for the flu season. The resulting shortage prompted U.S. health officials to put restrictions on who was eligible for flu shots.

The MHRA said inspectors believed improvements had been made and the facility now met satisfactory standards.

"The company has been informed and is now free to recommence full manufacturing of the vaccine," on the condition that it continue to make improvements at the plant, the agency said.

Chiron said it would provide weekly updates to the regulatory agency. Chiron spokeswoman Alison Marquiss said full production at the Liverpool facility was expected to recommence immediately.

"In this new beginning we remain focussed on continuing to remediate and improve so Chiron can successfully deliver on the results required to supply influenza vaccine for the 2005-2006 (flu) season," said Chiron Chief Executive Howard Pien.

Chiron's shares rose $3.34, or 9.4 percent, to $38.76 in afternoon trading on the Nasdaq Stock Market. They earlier rose as high as $41.10.

Last month, the biotechnology company reported a sharp drop in its fourth-quarter and full-year results on the back of the flu vaccine crisis. For the quarter that ended Dec. 31, the company lost $22.9 million, compared to a profit of $121.8 million a year earlier.