Washington

Plans to test a smallpox vaccine on small children in the United States have been slammed by critics who claim that the trial is unnecessary and potentially harmful.

The government wants to give 40 children, aged 2–5, doses of the Dryvax smallpox vaccine. Half would get a diluted form of the vaccine, and the rest would receive the full-strength version. The study, which would be funded by the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, would aim to assess the safety and efficacy of the diluted vaccine stockpile.

But the planned trial was greeted with a flood of criticism when details were posted on the website of the Food and Drug Administration (FDA) on 31 October as part of the public-review process.

The Department of Health and Human Services (DHHS) convened a panel of 10 experts — clinicians, lawyers and pharmacists — to examine the ethical questions raised by the proposed study. In their comments, which are also posted on the FDA's website, most of them agreed that there is a case for going ahead with the trials.

The study raises important questions, says Mary Faith Marshall of the University of Kansas Medical Center, who is former chair of the now-disbanded National Human Research Protections Advisory Committee and a member of the expert panel. For instance, she says, the risk of a smallpox attack is low, and an attack would probably affect just a few geographical regions. So most of the children who participate in the study will probably never be involved in an attack — and so would be unlikely to benefit from the study. On the other hand, between two and ten children out of every million could develop life-threatening side-effects from the vaccination.

Marshall points out, however, that the panel of experts recognized that the risk of an attack is not zero. And a smallpox attack would be deadly, killing about 30% of infected individuals. “That argues more strongly than if the mortality was not as high,” says Marshall.

But others disagree with the panel members' general approval of the proposal. They point out that despite the Bush administration's assertions that Iraq has stockpiles of smallpox virus, there is still no proof that it or other nations are planning to attack the United States with germs. And, they say, scientists are already developing a safer version of the vaccine, which will probably need to be tested in children anyway.

“The risks of the Dryvax vaccine are clear — and the fact is that death can occur even in normal, healthy children,” says Paul Offit, chief of infectious diseases at the Children's Hospital of Philadelphia in Pennsylvania and a member of the Advisory Committee on Immunization Practices, which advises the DHHS on vaccine policy. “There could be children who suffer from the vaccine who never had any chance of suffering the disease.”

And Al Sommer, dean of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, points out that young children are not at high risk of contracting smallpox in the event of a bioterrorist attack. Also, he notes, earlier experience with the vaccine indicates that young children are unlikely to respond to the vaccine differently from adults. “None of this makes any sense from a public-health perspective,” Sommer says.

The FDA is accepting public comments on the smallpox trials until 2 December. The federal health secretary and the head of the FDA will then issue a final decision on the trials.