The vaccines, which save millions of lives, are only made by a few companies. The regulatory restrictions that keep vaccines safe cause headaches for the manufacturers and the government has yet to formulate a better plan for stockpiling vaccines.

While everyone agrees that companies must be given better incentives to get into the vaccine business and stay there, coming up with a realistic way to do so is proving difficult.

The General Accounting Office, the investigative arm of Congress, issued a report Tuesday that said shortages of childhood vaccines forced 49 of the 50 states to ration shots in recent months.

It said the government had the authority to stockpile childhood vaccines, but had done so with only two and did not have a plan for creating stockpiles in the future.

"We are working on it," said Dr. Walter Orenstein, head of the National Immunization Program at the Centers for Disease Control and Prevention. "I think stockpiles are important, but they are not a panacea."

The main issue is that only four companies make most of the childhood vaccines, and that any one can drop out of the business at any time, Orenstein said in an interview. Or one can run into problems – one of the issues that caused this last shortage.

VULNERABLE SUPPLY

With five of the eight vaccinations made by one company each, this leaves the nation's supply highly vulnerable.

Even the vaccine makers, who have a virtual monopoly, say they would welcome competition. "I don't think anybody wants more competition from a business perspective," said Wayne Pisano, executive vice president of Aventis-Pasteur North America.

"But it is difficult for us to invest and expand. Changing the system will invite competition but it will also help us."

Still, no one is sure how to do that – by subsidizing vaccines, giving financial incentives, or simply by making the vaccine approval process easier.

The CDC recommends that all babies get 11 routine vaccines in eight shots. Over the past year, five vaccines have been in shortage – the MMR vaccine, pneumococcal disease vaccine, DTaP, the tetanus and diphtheria booster and chicken pox. Many are not fully effective until a child has received several doses.

Doctors have tried to give babies the vital first doses of vaccines, but in many cases have had to delay the last shots in the series to ensure that every baby gets at least some cover.

One problem was that some companies were having trouble producing enough supplies, but did not tell the CDC in time for the agency to get other makers to ramp up efforts. Companies could consider a supply shortage to be a trade secret and may be reluctant to tell the CDC.

Pisano hopes for even better communications with CDC.

"We believe CDC should have the power and authority to take confidential information and share it with other companies when there is a shortage," Pisano said in a telephone interview.

The GAO also suggested that the U.S. Food and Drug Administration be allowed to "fast-track" approval of new vaccines, an idea Orenstein favors.

Pisano had a final suggestion: make it harder to sue vaccine manufacturers.

The Vaccine Injury Compensation Program is supposed to be a no-fault insurance fund for people injured by the very rare side effects that vaccines have. But Pisano said some people are starting to sue companies directly, and Aventis-Pasteur was spending millions of dollars litigating 100 or so cases.