The controversial anthrax vaccine the US military wants to inject into millions of servicemen does not offer complete protection, it is reported.

Although vaccinated monkeys did not die from the disease after inhaling anthrax spores, they were still ill for two weeks.

This finding casts doubt on the usefulness of the vaccine to the military, as sick soldiers, like the wounded, hinder an army far more than dead ones.

The decision to vaccinate 2.4 million troops was taken after UN weapons inspectors operating in Iraq found that the regime had stockpiled 8,000 litres of anthrax spores before the 1991 conflict.

So far 450,000 members of the military have received the jabs - but several dozen have been court martialed after refusing to take the vaccine over fears about side-effects.

Chris Seiple, a former marine officer serving on a panel studying biological and chemical warfare at the Center for Strategic and International Studies, told the Washington Post: "People have been led to believe that you can be hit with this stuff and still be mission-ready.

"If you had a bunch of people taken prisoner because they were sick, you'd have a loss of public confidence."

Monkeys given anthrax

The laboratory tests at the US Army's Infectious Diseases Institute on rhesus monkeys involved 15 animals, 10 of which were given high doses of vaccine.

When all were then exposed to enough anthrax spores to kill, the vaccinated animals all survived, but were sick for a two-week period.

However, a scientist from the institute, Colonel Arthur Friedlander, described the idea that immunized animals exposed to anthrax were all incapacitated as a "gross overstatement".

He said other tests showed most animals did not become ill.

Naturally-occurring cases of anthrax are extremely rare, and generally happen when humans come in contact with meat from animals contaminated with anthrax spores.

More than 95% of naturally-occurring cases involve skin infection, and are rarely fatal.

However, if the spores are eaten or inhaled, death is much more likely - almost certain in the case of inhaled anthrax.