The conclusion was reached by two panels that studied the death of 22-year-old Rachel A. Lacy of suburban Chicago and the illnesses of three others, Defense Department officials said.
As is common practice inside and outside of the military, Lacy received several vaccinations in one day — for anthrax, smallpox, typhoid, hepatitis B and measles-mumps-rubella. The reservist got the shots March 2 at Ft. McCoy, Wis., and died a month later.
Two panels were convened at the Pentagon's request under the Health and Human Services Department. One reported last week that it tended to think, but couldn't conclusively prove, the vaccinations caused Lacy's death.
Members on the second panel differed, with three members saying it was "possible" the vaccinations were the cause and two saying it was "probable."
The panels found the illnesses of the other three people were not associated with the vaccinations, defense officials said.
Officials said Lacy's death was extremely rare and would not alter the Pentagon's vaccination program.
More than 900,000 service members have received the anthrax shot and more than 500,000 the smallpox shot — among the millions of doses of vaccines administered annually to protect troops against disease and bioterror threats.
Lacy, of Lynwood, Ill., was a nursing student before being called to active duty with the 452nd Combat Surgical Hospital Unit of Milwaukee.
One of the hospitals that treated Lacy diagnosed her with lupus, an autoimmune disorder.
Members of the two panels that studied the cases were all civilian physicians and academics who advise the government.
Worries about military vaccinations are not new. Since anthrax vaccinations were made mandatory for all U.S. military personnel in 1998, hundreds of service members have been disciplined or discharged for refusing to take the shot. At least 37 have been court-martialed.
For years, some parents have suspected the measles-mumps-rubella shot of causing autism or other severe health problems in children.
According to the federal Centers for Disease Control and Prevention, many vaccines carry an extremely small risk of adverse reactions that can lead to serious illnesses, and in an extreme minority of cases, even death.
The MMR jab causes severe reaction in one in a million kids who get it, the CDC says.
In the case of the anthrax vaccine, the CDC says "systemic reactions occur in fewer than 0.2 percent of recipients." Out of a million people who get the smallpox vaccine, 1,000 may have serious complications, between 14 and 52 will develop life-threatening problems, and perhaps one or two might die.