More flu vaccine (search) is expected to be available for millions of Americans in January, but that could be too late.

The flu season typically peaks in January or later. It takes two weeks for people to develop immunity after being vaccinated, which should be done in October or November, according to the Centers for Disease Control and Prevention (search).

So while the U.S. government is searching all over the world for more vaccine, it is unclear how helpful the extra doses will be if they don't arrive until next year.

Federal health officials said Tuesday that 2.6 million additional doses of flu vaccine will be available in January, far fewer than the 48 million lost to contamination at a British manufacturing plant.

"We're waging a comprehensive and aggressive response," Health and Human Services Secretary Tommy Thompson (search) told a news conference. "We have good reason to be optimistic in our ability to deal with the flu season and protect the most vulnerable from its harsh effects."

He said there was enough antiviral medicine available to treat 40 million people, shortening illness in people sick with the flu and preventing illness in healthy people.

Between vaccines and antiviral drugs, enough medicine will be available to treat 100 million people this flu season, Thompson said. Federal authorities have asked that healthy adults refrain from getting vaccinated to leave enough for those at greatest risk: the very young, the very old and people with chronic illnesses.

Sen. John Kerry, President Bush's Democratic challenger, has said the administration failed to heed warnings about a potential shortage.

"If you can't get flu vaccines to Americans, how are you going to protect them against bioterrorism? If you can't get flu vaccines to Americans, what kind of health care program are you running?" Kerry said.

In Florida, Bush sought to ease Americans' concerns. "I want to assure them that our government is doing everything possible to help older Americans and children get their shots despite the major manufacturing defect that caused this problem," he said.

Chiron Corp. was expected to provide the United States with 46 million to 48 million doses of flu vaccine, nearly half the supply the government anticipated needing. But British regulators closed Chiron's Liverpool facility because of contamination.

That left the United States with about 55 million doses from its second manufacturer, Aventis Pasteur. At a news conference Tuesday, Aventis Pasteur announced it could produce another 2.6 million doses.

The extra vaccine won't be ready for distribution until January.

Meanwhile, officials are looking "throughout the world" for additional vaccine, said Lester Crawford, Food and Drug Administration acting commissioner.

Crawford said the FDA would give expedited review to flu vaccine produced by ID Biomedical of Canada. The expedited review — "weeks, rather than months" — means the 1.5 million Canadian flu shots could reach Americans this season, he said. The agency plans to send its own inspectors to ensure the Canadian facilities meet U.S. manufacturing standards.

"We have similar standards," said Jirina Vlk, a Health Canada spokeswoman. She said she expected the FDA to have the Health Canada records by the end of October.