WASHINGTON - A laboratory test for the effectiveness of smallpox vaccines has been developed by a team of European researchers and it may be used as Americans start receiving shots against the disease.

In a study appearing this week in the Proceedings of the National Academy of Sciences, scientists in Germany and France report they have discovered a test that can determine if a candidate smallpox vaccine can prompt protection against the disease in humans.

The test could be used to determine if a person actually develops defenses against smallpox after being vaccinated. The large majority will develop immunity, but not everyone.

Dr. Bernard Moss at the National Institute of Allergy and Infectious Diseases, one of the National Institutes of Health, said the research is important because no scientist has ever identified in the human immune system the types of responses needed to protect against smallpox.

There was little interest in smallpox research after the disease was conquered worldwide in the 1970s, he said.

A detailed scientific study and understanding of the human immune system did not develop until the 1980s, long after interest in smallpox had waned, he said.

"This finding will be very useful," said Moss.

Researchers are developing new and safer smallpox vaccines, and the new laboratory technique can test the effectiveness of those vaccines.

Additionally, Moss said such a test could determine if people vaccinated against smallpox develop the immune system cells needed to protect against infection from the disease.

Smallpox shots were stopped in the United States in 1972, and the last natural case of smallpox is thought to have occurred in 1977. The disease was declared eradicated in 1980.

American officials believe some nations may have smallpox specimens that they could use to mount a bioterrorist attack. As a result, military personnel and some medical workers are expected to be vaccinated soon.

The vaccine will be available to the general public next year, but it is not recommended because of concerns about vaccine safety. It is estimated one to two people per million receiving the shot will die from side effects.

That's why researchers are trying to develop a smallpox vaccine that is as effective, but safer, than the current one.