WASHINGTON - A majority of states have scaled-back immunization requirements for school and day care programs because of a nationwide shortage of childhood vaccines, leaving open the possibility for disease to spread, a government report warns.

The report by the General Accounting Office, an investigative arm of Congress, was to be examined at a Tuesday hearing of a Senate Health, Education, Labor and Pensions subcommittee.

"It is clear from this report that we have a system that cannot guarantee an adequate supply of vaccines from year to year and is unprepared to handle a potential outbreak of many routine childhood diseases," said Sen. Jack Reed, D-R.I.

"We are putting our children in danger," said Reed, who was chairing the hearing. "We simply cannot allow decades of tremendous progress in reducing vaccine-preventable diseases to become undone."

According to the GAO report, 49 state and local immunization programs reported rationing one or more vaccines. Investigators surveyed 64 state, territorial and local immunization programs for the study.

"States reported that vaccine shortages and missed make-up vaccinations may reduce coverage and increase the potential for disease to spread," the investigators wrote.

The nation has experienced a shortage of childhood vaccines for the last two years, mainly because some manufacturers dropped out of the market while others had to slow production to upgrade their plants. At one point, the government reported a shortage in eight of 11 vaccines.

Doctors were notified by the Centers for Disease Control and Prevention in July that shortages were over for two vaccines, one for measles, mumps and rubella and another for diphtheria, tetanus and pertussis. And Tuesday's report said the CDC had advised that supplies for most vaccines were beginning to return to normal.

But the report warned that "the potential for recurring shortages will remain."

For instance, investigators noted there are still only a few companies that manufacture the vaccines. Five of the eight recommended childhood vaccines have only one manufacturer each.

The report also found that the CDC, which is required by law to stockpile a six-month supply of recommended childhood vaccines, only has stockpiles for two - one for measles, mumps and rubella and one for polio.

"In light of the recent shortages, CDC is now considering plans to expand the stockpile to include additional vaccines," investigators said.

The GAO is recommending to Health and Human Services Secretary Tommy Thompson that CDC address ways to expand its stockpiles. Investigators also say vaccines should be added to the types of products that can be considered under expedited review by the Food and Drug Administration.

ON THE NET

Senate Health, Education, Labor and Pensions Committee: http://labor.senate.gov/index.htm

C-SPAN will be providing live webcast of the child vaccine hearing. More info: http://www.cspan.org/watch/ .