Antiquated vaccine technology coupled with the vaccine's side effects, and the inoculation regime of six shots over 18 months "underscore the need for a new and improved alternative," says University of Pennsylvania epidemiologist Brian I. Strom, who chaired the committee.

Some have worried that advances in genetic engineering could produce a strain of anthrax resistant to the current vaccine. But Strom maintains that "natural mutations or bioengineered changes in the anthrax bacteria would not likely produce vaccine-resistant strains."

Bioport Corp. of Lansing, Mich., the sole manufacturer of the U.S. vaccine, was cited by FDA for poor manufacturing practices and shut down in 1998. The plant was allowed to reopen this January after extensive renovations. The vaccine, largely reserved for military personnel, is in short supply. But nearly 200 civilians were inoculated after last fall's mail-delivered anthrax attacks that killed five people and sickened 13.

In 1998, the Pentagon halted its all-troops inoculation program because of the shortage. Controversy fueled by the refusal of more than 400 troops to take the vaccine--because they feared it caused symptoms similar to Gulf War syndrome--also influenced the Pentagon's decision.

The IOM study finds that adverse reactions associated with the anthrax vaccine are no more prevalent or severe than similar reactions seen with other vaccines. Publicly available data do not confirm long-term health risks. But the committee cautions that data are limited and urges the Pentagon to monitor for long-term effects of this and other vaccines.

Meryl Nass, a physician in private practice in Freeport, Maine, who has researched anthrax for 13 years and who has testified repeatedly before congressional and IOM committees, believes the Pentagon has substantial data on the long-term effects of the vaccine. But she believes "the data are so damaging that the Pentagon won't release them." She also says available studies have not convinced her that the vaccine is effective against inhalation anthrax.

The IOM endorsement paves the way for the Pentagon to resume its mass vaccination program. In a statement, Assistant Secretary of Defense for Health Affairs William Winkenwerder Jr. said the IOM study confirms the Pentagon's use of "a protective measure that works for those at risk to exposure to lethal agent anthrax."

Side effects from the anthrax vaccine result from it being injected under the skin instead of into muscle, and from the number of inoculations needed for immunity. Strom says a Centers for Disease Control & Prevention study is testing the efficacy of injecting fewer shots into muscle.

Still, the committee urges the Pentagon to accelerate research that it is conducting with NIH on new anthrax vaccines. Ideally, the new vaccine should require only two or three injections, produce immunity quickly and for at least a year, have a long shelf life so it can be stockpiled for use when needed, and produce no severe side effects.

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