If the United States wants to avoid future shortages of flu vaccine it must take steps to draw drug companies back into the business of making the inoculations, flu experts say.

In a bad year, the stakes could be higher than just saving people from fever, headaches and a runny nose.

“What if you had 20 or 30 percent of your population not able to go to work or to school? It would affect the economy. It would affect, in a sense, our security,” said Dr. Gregory Poland of the Mayo Clinic, who sits on a federal vaccine advisory board.

Health officials warned of shortages last Tuesday after one of the two companies that supply most of the nation’s flu inoculations said it couldn’t provide any. British authorities had suspended the license of Chiron Corp. because of problems at its vaccine plant in Liverpool. That chopped the nation’s supply of flu vaccine in half.

When the news reached a meeting of vaccine experts Tuesday morning, “we were shocked and surprised, and then we got depressed, and then we just moved into problem-solving,” recalled Dr. William Schaffner of Vanderbilt University.

“It doesn’t help the firemen to get angry at the fire, you’ve got to go to work and put it out.”

The basic problem is that “we’ve lost most of our domestic manufacturers” of flu vaccine, said Richard Webby at St. Jude Children’s Research Hospital in Memphis. “When you’re relying on two manufacturers ... and one goes down, you’re up the creek.”

Drug companies have pulled out of flu vaccine production because it’s not very profitable and it’s financially risky, health experts said.

One big problem is that demand for flu shots fluctuates from year to year as public interest waxes and wanes. Last season brought huge demand for a flu shot; the year before saw little interest, Poland said. But flu shots have to be made far in advance, so the manufacturers must rely on estimates and then they’re “out there naked in the marketplace,” said Schaffner.

If a flu shot isn’t used during the season, it must be discarded. So companies generally throw away millions of doses a year, Poland said.

What’s more, making vaccines requires massive capital investment and involves the costs of complying with federal regulations, and the market is relatively small, he said.

So what can be done to draw more companies into making flu vaccines?

One strategy would be to make demand higher and more reliable by getting more healthy adults to get flu shots regularly, Webby said. Between the publicity over last year’s early flu season and the current concern that bird flu could spawn a lethal human pandemic, “flu certainly has had a relatively high profile the last couple years,” Webby said. “All of this I think is certainly raising public awareness.”

Other experts suggest having the government commit to buying a certain number of doses at a given price each year, buffering the uncertainty. Currently, most flu vaccine in the United States is bought by the private sector.

Not only could government buy more flu vaccine and promote flu shots more aggressively, it could also require health insurance companies to cover flu shots as well as other vaccines for adults, Schaffner said. A companion public program could provide flu shots for uninsured people, he suggested.

“It would create a huge new market.”

By next year, a guaranteed government purchase might ensure that the three flu vaccine makers that now supply the nation remain in the business, Poland said. Besides the two major suppliers, another company makes the new inhaled vaccine, FluMist.

Poland said other measures also could improve the financial picture for manufacturing flu vaccines, such as easing the cost of complying with regulations and speeding up approval of new vaccines.

Schaffner said it’s important for the government to keep focused on the problem.

“We need to not let our attention flag once this crisis is behind us,” he said. “We need to keep our eye on the ball here.”

The shortage has forced health officials to ration the available inoculations. The flu shots are now for people 65 years of age and older, babies six to 23 months old, nursing home residents, pregnant women, day care workers and people with compromised immune systems. Healthy people are being asked to take a flu mist instead. That’s still not enough to counter the rush or cut the lines down.