The move is part of a widening revolt in medical circles against the White House vaccine program. Coincidentally, that program is led by Centers for Disease Control and Prevention Director Dr. Julie Gerberding, who ran the infection control programs at San Francisco General before joining the CDC in 1998.

Initially, federal planners hoped to vaccinate 500,000 doctors and nurses who would be the first line of defense against a bioterrorism attack.

But because the vaccine itself is an infectious agent -- a virus that causes vaccinia, or cowpox -- it is potentially dangerous to those sensitive to that disease. There is also a risk that newly immunized health care workers,

for two to four weeks after vaccination, can accidentally transmit cowpox to patients.

Vaccinia typically stirs up a strong antibody response that protects against smallpox. But vaccinia can sometimes cause a life-threatening, runaway infection, particularly in people with weakened immunity.

Dr. Susan Fernyak, director of communicable disease prevention and smallpox planning for the San Francisco Department of Public Health, said the purpose of the policy restricting vaccinations is to protect those patients.

"We didn't want anyone who is vaccinated, and still infectious, to be working with patients directly," she said. "We have a high number of patients with HIV, with certain skin conditions, with cancer, with transplanted organs or who are taking immunosuppressive agents."

Under the policy, city health care workers who have "direct contact" with patients are forbidden to receive the vaccine unless they can find a way to avoid patients. They must do so until the blister from the vaccine on their arm is no longer infectious -- at least two to four weeks.

NO TIME TO SPARE
But Fernyak acknowledged that, due to the chronic shortage of nurses and tight budgets, almost no one in the hospital can be relieved from patient care duty for that length of time.

Throughout the health department, about 15 doctors and administrators have juggled schedules so they can be vaccinated, she said. Nurses are unlikely to be able to do the same.

Gerberding declined to comment on San Francisco's smallpox vaccine policy, but CDC spokesman Tom Skinner said cities should not gloss over the risk of bioterrorism. Gerberding, he said, "has been participating in meetings where a certain level of intelligence has been shared, and she's saying that, without a doubt, we're doing the right thing."

Skinner said the reluctance of many hospital workers to be vaccinated could be shortsighted. "Here's the problem: I don't think anyone knows what an attack will look like," he said. "Would it be one case in Middletown, USA? Or a thousand cases at different locations? Or a thousand cases in one location? You must have people in place to vaccinate people."

While most nurses at San Francisco General appear to support the city's stance -- and are firmly backed by their union -- there are some who want to be vaccinated.

"We're all health care professionals. We can make decisions for ourselves. You don't get to be an ER nurse without having some brains," said one emergency department nurse, who asked to remain anonymous.

RISK VERSUS BENEFITS
"There are two chances in a million of dying from a vaccine," the nurse added. "What are the chances of a terrorist attack?"

A study by Rand, a Santa Monica think tank, estimated that the nation's 10 million health care workers, who make up 3 percent of the population, could account for as many as half of the nation's smallpox cases in the event of an attack.

But across the nation, only about 7,354 civilians have been vaccinated under the program to date. Labor unions are actively urging their members not to volunteer for the vaccine.

Nurse union activists say the overwhelming majority of nurses at San Francisco General support the policy -- in fact, the Service Employees International Union Local 790 was among the first to criticize the vaccination plan.

"My feeling is, we don't ask the health department, which is scarce on resources, to pay for other people's paranoia," said Lorraine Thiebaud, vice president of Local 790. "If you want to get the vaccine, and you've got vacation time on the books, go out and use it."

For every 1 million people vaccinated, according to the CDC, between 14 and 52 will experience a severe reaction, and one or two will die of it. Among that same group of people, there will be 20 to 60 cases of accidental transmission to someone who comes in contact with them.

ACCIDENTAL INFECTION
Last week in Los Angeles, an unidentified patient was hospitalized with an accidental cowpox eye infection, apparently contracted from someone recently vaccinated in the military.

Across the country, the issue of compensating health care workers for time lost if they are made ill by the vaccine looms as the largest threat to the federal program. CDC spokesman Tom Skinner said the agency "is getting closer and closer" to releasing a plan to address those concerns.

But federal disease control experts do not believe the vaccination itself poses a significant threat to immune-compromised patients. Last week, the Advisory Committee on Immunization Practices published revised recommendations,

reiterating that proper bandaging and other infection control procedures should "essentially eliminate" the risk of infecting a patient.

With union hospital workers reluctant to be vaccinated, medical giant Kaiser Permanente has put on hold its plans to give the vaccine to its first- response staffers. Under a "labor-management partnership" pact, Kaiser is negotiating with its unions over issues such as compensation for lost time due to vaccine-related illness.

"There are some details that still need to be negotiated," said Dr. David Witt, chairman of the infectious disease program for Kaiser in Northern California.

Witt said Kaiser doctors may be more willing to be vaccinated than unionized workers, because physicians have "a better disability package than the average union worker." Nevertheless, he said some staffers at his South San Francisco hospital are eager to be vaccinated. "Some of them are quite angry, but I told them we can't go."