The nation's supply of vaccines against infectious diseases is in jeopardy and may not recover without major shifts in the way the country pays for them, according to a series of reports released Tuesday.

The studies appear in the May/June edition of Health Affairs. They detail what experts have long known: Unstable demand, increasingly costly production, and the threat of lawsuits are making companies more and more reluctant to manufacture vaccines against a host of childhood and adult diseases.

Meanwhile, the price of vaccines for the general public -- many of whom lack insurance coverage for immunizations -- continues to rise. The dynamics have left the U.S. vulnerable to a repeat of last year's flu vaccine shortage that left the country without roughly half of its needed supply of shots when one of only two suppliers failed to ship its products.

Many Vaccines, Few Makers

The CDC recommends that most U.S. children receive eight vaccines against 12 diseases by the time they reach 18 months of age. Flu and pneumonia (pneumococcal) vaccines are recommended for many adults into old age.

Only five domestic manufacturers make vaccines against these illnesses, leaving only a sole supplier for many required immunizations.

The U.S. has faced intermittent shortages to its supplies in recent years. As was the case with last year's flu vaccine disruption, health officials are forced to scramble when manufacturing or safety problems at one company's plant leave no other supplier.

Such was the case in 2001 and 2002, when shortages in five vaccines used to prevent eight diseases caused rationing and forced the government to dip into its emergency vaccine stockpile.

And that stockpile itself is not safe. Three manufacturers told government officials in April that they would no longer keep vaccines in the reserve for the stockpile because of accounting regulations that don't let them list those vaccines as sold. The glitch has left the stockpile with less than a third of the 14 million doses it is supposed to hold.

Vaccines and Lack of Money

"Unless financing challenges are addressed, many children may not receive the full benefit of these vaccines," write Walter A. Orenstein, MD, and colleagues. Orenstein is director of the program for vaccine policy and development at Emory University.

Manufacturers complain that declining financial incentives in the U.S. market make it hard for them to justify spending the hundreds of millions of dollars it can cost to develop new immunizations. They also say the threat of legal action from patients allegedly injured by vaccines also puts a damper on investment.

"The development and delivery of new and existing vaccines -- both in the United States and globally -- remain a formidable challenge," writes Adel Mahmoud, president of Merck Vaccines.

Paying for Coverage

The federal government buys nearly 60 percent of all childhood vaccines produced in the U.S. as a way to protect against unreliable supplies and keep prices under control. Manufacturers make up for the suppressed prices by charging inflated rates for vaccines delivered with financing from private insurers.

Those prices continue to rise. This year, it cost an average of $782 to fully immunize a child according to CDC guidelines, say Orenstein and colleagues.

Rising costs have driven more and more insurers to omit vaccinations from their basic insurance plans. According to another study published Tuesday, some 5 million children and 36 million adults with private medical coverage do not have insurance for vaccinations.

"This means that new vaccines in the future may be available to many people only if they can pay out of pocket," write Matthew M. Davis, MD, an assistant professor of pediatrics at the University of Michigan, and colleague.

Nearly 80 percent of 995 adults surveyed by Davis and his colleague said they would be willing to pay more for insurance if it guaranteed them access to childhood immunizations. Nearly half said they would pay more for adult immunizations.

By Todd Zwillich, reviewed by Michael W. Smith, MD

SOURCES: CDC. Orenstein, W. Health Affairs, May/June 2005; vol 24: pp 599-610. Mahmoud, A. Health Affairs, May/June 2005; vol 24: pp 596-597. Davis, M. Health Affairs, May/June 2005; vol 24: pp 770-779.