ATLANTA (AP) -- So few health care workers are choosing to be vaccinated for smallpox that the federal government is worried how it would counter an attack of the deadly virus.

About 37,600 health workers nationwide have been immunized since the new vaccination program began in January. Thousands were being inoculated weekly in the early going, but by May the number dwindled to 100 or so a week, officials with the Centers for Disease Control and Prevention said Wednesday.

Only 40 percent of the country's acute care hospitals have vaccinated at least one hospital member. Only about 10 percent of hospitals have 25 or more staff members vaccinated.

"If we had an outbreak today, we would clearly need unvaccinated staff to help" contain the disease, Dr. Walter Orenstein, director of the CDC's National Immunization Program, said at a briefing of the agency's Advisory Committee on Immunization Practices.

"We are extremely vulnerable right now," said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. "If a single case shows up ... we are not prepared for that."

The officials attributed the dropoff in vaccinations primarily to states reviewing the program before offering shots to police, fire crews and other first responders.

With the Iraq war winding down, some health care workers are opting not to be vaccinated now because they believe the threat of a smallpox attack is small.

Others don't want to be inoculated because of concerns over rare but serious side effects. Since January at least 21 people have reported severe health problems after being vaccinated. Most recovered, but six had heart attacks and two died.

Smallpox was declared eradicated from the world in 1980 but U.S. officials believe it could exist for use as a bioterrorist weapon.

Copyright 2003 The Associated Press. All rights reserved.