The government is pressing to buy more flu vaccine (search) despite a slow start to the flu season.

The Food and Drug Administration has signed off on the safety of a portion of 5 million doses that are available from plants in Canada and Germany. Health and Human Services Secretary Tommy Thompson was scheduled to announce the vaccine purchase Tuesday.

The FDA has inspected the facilities where the vaccines were made. The agency also tested that they would be effective against the dominant flu strain expected in the United States and made sure the vaccines have been stored properly since they were made, HHS officials said Monday.

They spoke on condition of anonymity in advance of Thompson's announcement.

Earlier Monday, the director of the Centers for Disease Control and Prevention cautioned health care officials to remain alert even though the flu season has begun slowly, with no widespread outbreak reported.

But health care officials were urged to remain alert.

"A slow start doesn't necessarily reflect a slow season," Dr. Judith Gerberding, director of the CDC, said at an American Medical Association conference in Atlanta. "The most common month of peak activity is February."

The FDA has been working since October to arrange for additional flu shots that were not made for U.S. consumption.

Canadian flu shot maker ID Biomedical has just over 1 million doses to sell to the United States, while British drug manufacturer GlaxoSmithKline can provide 4 million doses from a German plant, Thompson said in October.

Officials declined to say how much vaccine was being purchased now.

Separately, Illinois, New Mexico and New York City have located another 650,000 doses from drug wholesalers, but have not yet gotten FDA approval to purchase the vaccine for their residents.

Health officials had planned to have more than 100 million doses of the vaccine this season, the biggest supply ever. But flu shot maker Chiron Corp. (search) announced Oct. 5 that it could not ship its 48 million doses after British health officials suspended its license because of contamination at a Liverpool plant.

The resulting shortage was a major concern to physicians at the AMA meeting who complained that the flu vaccine was at times available on a first-come basis instead of reaching high-risk patients as a top priority.

However, Gerberding said, "volunteerism works" as most Americans followed CDC guidelines for reserving the vaccine for those in greatest need.

"The people who should step aside stepped aside," she said, adding that she does not endorse penalizing healthy patients who are taking the vaccine.

About 61 million doses have been available this season, including a nasal vaccine only for healthy people ages 5-49. The CDC has said 98 million people, including 9 million children, need the vaccine.

Each year, the flu kills about 36,000 people in the United States and sends another 200,000 to the hospital.