North Dakota health officials are working with public and private health care providers to monitor the state's flu vaccine supply.

The state Department of Health is waiting for guidance from the U.S. Centers for Disease Control how to handle an expected shortage of the vaccine. British health officials Tuesday pulled the license of Chiron Corp., which produces half of the United States supply. The company planned to ship 46 to 48 million doses this year.

British officials didn't explain details leading to the action taken against Chiron, but company officials said that the decision came because of broad concerns about standards at its Liverpool factory.

Health care providers in the state had ordered doses from Chiron and Aventis, another manufacturer of the vaccine. State Epidemiologist Larry Shireley said that the department is waiting to hear from the CDC whether other manufacturers of the vaccine will increase their production.

"We have a lot of unanswered questions right now," Shireley said. "A loss of half of the vaccination supply at this stage is significant."

The Associated Press reported Aventis - which expects to supply 52 million doses - wouldn't be able to produce more vaccine until after November, when existing orders are filled. The maker of FluMist said it couldn't make more than the 1.5 million doses it planned to manufacture this flu season.

Most health providers start flu-shot campaigns in October, which is about a month before the flu season typically begins. Last year, the state reported 1,663 cases of influenza. Shireley said that was a record number of cases, and he expected to see an increased demand for the vaccination this year because of last season.

Until the announcement today, state officials were urging all residents to get vaccinated because they expected a large supply. Shireley said he expects doses will be rationed, with high risk individuals receiving priority. The state is waiting for guidance from the federal government before making a final decision.

People who have underlying medical conditions, are at least 14 weeks pregnant or aged 65 or older are considered to be high risk.

"The bottom line is we will have to see what the guidance will be and what the vaccine supply is going to be," Shireley said.

Bismarck Burleigh Public Health director Paula Flanders said the organization planned to start weekly shot clinics Oct. 14 but now it is waiting for direction from the state, which is expected to come within a couple of days.

"We have had flu vaccine problems for the last three years," Flanders said. "Each year we think next year will be better, and we won't have to deal with this unknown. And here we are again."

(The Associated Press contributed to this report. Reach reporter Sheena Dooley at 250-8225 or sheenadooley@ndonline.com.)