WASHINGTON (Reuters) - U.S. plans to vaccinate a front-line team of health workers in case of a smallpox attack are moving so slowly that the results cannot even be evaluated for safety, according to a government report issued on Wednesday.

The report from the General Accounting Office (GAO), the investigative arm of Congress, echoes earlier findings from groups such as the independent Institute of Medicine (IOM).

The IOM found that health-care workers were afraid to be vaccinated without guarantees that they and their families would be cared for if they suffer side effects from the vaccine, which kills about two of every million people who get the shot.

"Implementation of the smallpox vaccination program has proceeded more slowly than CDC planned," the report reads.

Only about six percent of the targeted workers have been vaccinated, it found.

"Because of the slow pace, not enough data were generated by week 10 to evaluate whether the program is proceeding as safely as possible," the report said.

The original smallpox vaccination plan by the U.S. Centers for Disease Control and Prevention (CDC) called for 500,000 doctors, nurses and other health workers to be vaccinated. They would then be ready to vaccinate up to 10 million others.

As of April 18, the CDC reported, 33,444 civilians had been vaccinated against smallpox. The military is also vaccinating up to 500,000 troops.

"CDC has reconsidered the initial targets and said that as few as 50,000 vaccinated health workers nationwide would provide sufficient response capacity," the GAO report said.

"But as of late April, CDC had not set a new nationwide target or requested that the 62 jurisdictions adjust their targets for numbers and types of vaccinated health workers and distribution of response teams."

The report also said CDC sent confusing advice to the states and cities.

Smallpox was the first disease ever to be eradicated -- by vaccination in 1979 -- but the U.S. government fears smallpox weapons exist and could be used.

Because smallpox kills about 30 percent of its victims and because no drugs are licensed to treat it, vaccination is considered the best way to defend against it.

HIGH RATE OF SIDE EFFECTS IN THE PAST

Before widespread vaccinations in the U.S. were stopped in 1972, the shot had a high rate of side effects. The CDC reports that 10 people recently vaccinated had serious heart side effects that could be related to the vaccine, and three died.

It also reports nine cases of generalized vaccinia -- a skin infection caused by the live virus in the vaccine. This live virus, called vaccinia, is related to the smallpox virus.

The report, published on the Internet at http:/www.gao.gov/highlights/d03578high.pdf, says so few people have been vaccinated in the current campaign that it is impossible to say whether an unusually high number of people suffered side effects.

It notes that many health-care workers are worried about the risks to themselves and their families -- and fear they will not be cared for or compensated if they die or suffer a complication. It also said the program schedule was demanding.

"CDC and HHS (Health and Human Services Department) have been working to address the major challenges, but to date they have not been able to overcome them," the report reads.

"Unless these efforts succeed in overcoming the hesitancy of the participants, it may be difficult to achieve the targets in the first stage."

Congress is considering a package that would compensate volunteers hurt by the vaccine.