Randomly selected guard and reserve troops surveyed in 2000 by the General Accounting Office also reported adverse reactions to the vaccine at double the rate claimed by the manufacturer, BioPort Corp., the GAO said.

    Military members who have left represent some of the most experienced and highly trained individuals in the Air National Guard and Air Force Reserve "and are people not easily replaced," the GAO said.

    "While many factors can and do influence an individual's decision to participate in the military, a significant number of pilot and air crew members cited the required mandatory anthrax immunization as a key reason for reducing their participation or leaving the military altogether in 2000," the GAO said.

    The GAO recommended that Defense Secretary Donald Rumsfeld require a surveillance program to monitor problems with the vaccine. The program should ensure complete and appropriate treatment and follow-up for those who experience problems or who may have them in the future, the auditors said.

    In a response included with the report, the Defense Department disagreed with the GAO's recommendation and some of its findings.

    Reginald J. Brown, assistant secretary of the Army, cited a National Academy of Sciences report that concluded there was no data that pointed to the need for a monitoring program. Brown also said the GAO's findings on rates of separation by pilots were not supported by data from the Defense Manpower Data Center and the GAO did not consider normal turnover rates.

    The GAO mailed 1,253 surveys in May 2000 and received 843 responses, with 833 providing useful information. The surveys were developed with the help of pilots and other aircrew members of the Air National Guard and Air Force Reserve.

    The survey was conducted at the request of Rep. Dan Burton, R-Ind., chairman of the House Government Reform Committee.

    "Anthrax is a serious threat that our soldiers might face on the battlefield. At the same time, this vaccine has been controversial, and it has caused serious reactions in some individuals," Burton said in a news release.

    Anthrax is an acute infectious disease caused by spore-forming bacteria. Five people were killed in last year's anthrax attacks by mail. It is considered to be a possible biological weapon that could be used against U.S. troops.

    Hundreds of thousands of U.S. troops have received vaccines to protect them against anthrax, particularly during the Persian Gulf War. After a long pause in the inoculation program, the pace of vaccinations was accelerated last month, officials said. Some veterans and researchers believe the vaccine is partly responsible for illnesses reported by Gulf War veterans.

    According to the GAO survey, between September 1998 and September 2000, about 16 percent of guard and reserve pilots and air crew had moved to inactive status, left the military or transferred to another unit -- mostly nonflying positions to avoid or delay receiving anthrax shots.

    About 18 percent of those in or assigned to a unit indicated they planned to leave soon. The GAO said both groups ranked the anthrax vaccine as a key factor in their decision.

    About 45 percent said they would consider returning if the anthrax immunization were voluntary.

    The GAO estimated that about 37 percent of the service members surveyed had received one or more anthrax shots as of September 2000. Of those, 85 percent reported experiencing some sort of reaction, far higher than the 30 percent claimed by the vaccine manufacturer.

    Each shot generated an average of four or more reported reactions, some that could have negative effects on the service member's job, the GAO said.

    The GAO said it found two DOD studies of the vaccine, one in Korea and one in Hawaii, that reported similar reaction rates.

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