WASHINGTON (AP) _ Federal officials prepared to ship smallpox vaccine to about a dozen states as a scientific advisory panel urged them to move cautiously. The panel said reactions to the first round of inoculations should be analyzed before giving shots to millions of health care and emergency workers.

The scientists also recommended that health workers being offered the vaccine be told that it carries real risks, and that they are likely to receive only minimal compensation if they are injured.

``The committee suggests explicitly stating that the benefit of the vaccination program is to increase the nation's public health preparedness, but that the benefit of vaccination to any one individual might be very low,'' the panel convened by the Institute of Medicine reported.

The last case of smallpox in the United States was more than 50 years ago. Routine vaccinations here ceased in 1972, but experts fear the disease could return in an act of bioterror.

Still, the risk of such an attack is unknown, and the chances that any given person will encounter the virus are particularly small, the Institute of Medicine noted. Meantime, the risks of the vaccine are well documented: Based on historical information, as many as 40 people out of every million being vaccinated for the first time will face life-threatening reactions, and one or two will die.

A plan announced last month by President Bush calls for quickly vaccinating nearly a half million people working in hospital emergency rooms and on special smallpox response teams, with inoculations set to begin next Friday. With little time remaining, the panel recommended a series of safeguards aimed at educating people who may receive the vaccine, tracking their reactions to it and communicating with the public about the smallpox program.

Officials at the Centers for Disease Control and Prevention said they were confident that people offered the vaccine would be given the information they need and that they would carefully track reactions.

``Protecting the public is our core business and it's certainly our highest priority,'' said Dr. Julie Gerberding, CDC director.

Chiefly, the committee said, people being offered the shot must understand that they are helping to prepare the nation should bioterrorism strike _ unlike other vaccines which primarily protect the person getting the shot.

The experts also recommended that people be specifically told that they may not receive any compensation if they are injured by the vaccine.

Congress acted to protect people and institutions delivering the vaccine from most lawsuits that could be filed by those injured by the inoculation, leaving such patients with little recourse. Under the policy, injured people may have access to state workers' compensation programs, but those programs are not likely to cover all medical expenses and time lost from work.

An existing compensation fund helps people injured by other vaccines, but it does not cover smallpox. So far, the administration has not proposed any similar fund for smallpox.

Without a way to reimburse people for their lost work time and medical expenses, the panel said, ``some, perhaps many'' people may decline to get vaccinated, undermining the effectiveness of the program.

Gerberding said the administration is working on the problem but didn't have a solution yet. In the meantime, she said, ``we are certainly not going to delay this program because of concerns about compensation.''

Similar concerns were voiced Friday from Capitol Hill. Several Democrats, including House Minority Leader Nancy Pelosi, called on Bush to create a compensation fund for people injured by the vaccine, saying it was ``manifestly unjust'' to deny help for health care workers who are hurt because they stepped up to help the nation prepare for a bioterror attack.

The first phase of the program is set to begin next Friday, and Gerberding said CDC planned to ship more than 50,000 doses of vaccine to 11 states on Tuesday, as of Friday afternoon. She would not name them, but officials in South Dakota, Pennsylvania, Colorado and New Hampshire were among those who said they had placed their orders.

The Institute of Medicine also recommended that federal officials move slowly to the program's second phase, when the vaccine will be offered to some 10 million people, including other health care workers and emergency responders such as police and firefighters.

Friday's report recommended that the CDC evaluate the rate of serious reactions, the effectiveness of its educational material and the variation in vaccination policies from round one before moving to the second group of vaccines. It said the CDC also needs a more aggressive monitoring system to track reactions to the vaccine.

The CDC also should name a ``single voice'' to communicate with the public _ someone with a strong scientific background and widely recognized credibility, the panel said. That person, the panel added, ``should not be a politician.''

During the 2001 anthrax attacks, the Bush administration was roundly criticized for inaccurate information given by politicians. Many say that the situation improved markedly after scientific experts took the lead in communicating with the public.

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On the Net: Government smallpox information: http://www.smallpox.gov

Institute of Medicine report: http://www.nationalacademies.org