Researchers at Cincinnati Children's Hospital Medical Center and Harbor-UCLA Medical Center in California want to know whether diluted smallpox vaccine is effective in children aged 2 to 5. The only way to know for sure is to test the vaccine in a small group of children. It's the same way that nearly all medicines are tested.

Smallpox vaccine is effective. It is made from the bacteria that causes a less serious but related illness, cowpox. The body makes antibodies to it which fight smallpox. Similar vaccines have been used for more than 200 years.

There hasn't been a case of smallpox reported in the world since 1977. But smallpox is again a world concern because it's possible that some nation or group would use it as a biological weapon to infect and kill soldiers and civilians in other countries.

In preparing for such a possibility, it's been found that a diluted vaccine works in adults. But the diluted vaccine's effectiveness is not known in children.

So a test study has been proposed, using 40 children who would be volunteered by their parents - 20 in Cincinnati, 20 in Los Angeles. Because of the war against terrorism, the plan has attracted public attention. There is a 1 in 1 million chance that a child could die from the vaccine and a 3 in 1 million chance of causing encephalitis.

But questions over the ethics of using children in a study of medicine that may never be used sent the proposal to a government agency. The Office for Human Research Protections, a unit of the Department of Health and Human Services, is expected to render a decision in early 2003 on whether the study should be done.

The risks in this study are the same kinds involved in testing other medicines. Nearly every medicine that is approved for human use has already been tested, usually on animals and then on humans. It's the only way to find out for sure how well the medicine works and what side effects it may have.

Yet vaccinating children before they go to school has been well-established public health policy for generations. It's likely that many of the children will never be exposed to some of the diseases they've been vaccinated against.

It's the principle of being prepared for possible infection.

The risk of this test is small, the benefits obvious. It is doubtful that those who oppose this testing program would really want to use an unproven vaccine after a nation's children are exposed to deadly smallpox and hope it works.

The government, assuring that all appropriate controls are used, should allow this test to proceed.