ARLINGTON, Va. — The Pentagon cannot force troops to take the anthrax vaccinations against their will, according to a federal judge, who issued a temporary injunction Monday.

Until proven otherwise by the Food and Drug Administration, U.S. District Court Judge Emmet G. Sullivan in his 34-page decision agreed with the plaintiffs’ contention that Anthrax Vaccine Absorbed is still an unlicensed, investigative drug and being used for an unapproved purpose, and thus violates a 1998 federal law that bans the use of certain experimental drugs.

The federal government approved the vaccine three decades ago.

But plaintiffs in the class action suit — unidentified active duty, National Guard and civilian defense employees — say the license does not include approval for use against inhalation anthrax.

The Pentagon maintains that the vaccine is not experimental and that it is licensed for protection against anthrax whether it is inhaled or absorbed through the skin.

Because the matter is still under litigation, Pentagon officials referred all questions to the Justice Department.

“No determination has been made on what the next step will be on behalf of the United States,” said Justice spokesman Charles Miller. The department can choose to appeal Sullivan’s decision.

However, the injunction as of Monday is temporary, and Sullivan in his ruling scheduled a March hearing in his chambers.

“The judge asked a lot of questions in his ruling, and the onus has been placed on the government to prove its decisions,” Miller said.

Sullivan noted that the label on the vaccine does not specify which method of anthrax exposure it protects against.

Congress passed the law amid fears that the use of such drugs may have led to unexplained illnesses among veterans of the 1991 Persian Gulf War, which have come to be known as Gulf War Syndrome.

“The women and men of our armed forces put their lives on the line every day to preserve and safeguard the freedoms that all Americans cherish and enjoy,” Sullivan wrote.

“Absent an informed consent or presidential waiver, the United States cannot demand that members of the armed forces also serve as guinea pigs for experimental drugs.”

Forcing troops to take the vaccine would require a special order from the president, who issued no decision.

“It’s too early to speculate with the ruling just being today,” said White House spokesman Allen Abney.

Pentagon officials, caught off guard by the ruling coming out the week of Christmas, had no official comment.

The suit, filed in federal court by “John Doe,” a representative of the military population, sued Defense Secretary Donald Rumsfeld, Secretary of Health and Human Services Tommy Thompson, and the Commissioner of the Food and Drug Administration Mark McClellan.

In spite of protests by servicemembers who for years have said the vaccine has made them ill, Pentagon health officials have maintained the vaccine is safe with equal fervor.

Many servicemembers risked careers and freedoms to boycott taking the vaccine, and more than 400 personnel have been disciplined since the shot was made mandatory in 1998, including some who have been jailed.

Right now, servicemembers take a series of six shots over 18 months, along with an annual booster. Part of the issue surrounds a substance called squalene, which makes vaccines works faster and longer, but has not been approved by the FDA to be used in the anthrax vaccine.

Shots started in 1998 for soldiers in areas believed to present the highest risk of infection — the Persian Gulf, then South Korea.

The anthrax vaccine itself has been approved by the Food and Drug Administration since the 1970s and used regularly to protect veterinarians and scientists working with anthrax.

While the government does not recommend vaccinating the general public, it says the vaccine overall is very safe, with rare severe side effects such as dangerous allergic reactions.

But hundreds of military personnel have refused the shots, worried they could be connected to complaints of chronic fatigue, memory loss and other problems.

— The Associated Press contributed to this report.

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