This is no ordinary vaccine.

To inject patients with the smallpox vaccine, nurses jab them not once but 15 times in a 5-millimeter area. No wonder President Bush's call the vaccination of health and emergency response workers -- in case of a terrorist attack using the smallpox virus -- requires a special training effort.

Gloria Collins, a Loudoun County public health nurse, recently traveled to the National Centers for Disease Control and Prevention in Atlanta for instruction in training others to train still others to administer the smallpox vaccine.

Collins, 59, of Winchester, was one of four Virginia nurses and 240 nationwide to attend the "vaccinators workshop." She will be responsible for training all Northern Virginia nurses designated to teach their own staffs how to give the vaccination.

David Goodfriend, director of the county health department, said Collins was selected for her teaching experience, not because of any particular risk in Loudoun.

"We do have an international airport in the area and one up at Baltimore," he said. "We are at risk, but whether we're at risk more than anywhere else in the United States, I can't answer that question."

Collins has taught nursing students at Shenandoah University and was a nurse manager in the Lord Fairfax health district before coming to Loudoun Health Center 12 years ago. She has received the smallpox vaccine twice, as a child and before beginning nursing studies. After 10 years, she explained, the vaccine no longer prevents smallpox but usually prevents fatalities.

The vaccine is administered with a bifurcated needle. It "looks like a pitchfork with two prongs on it," Collins said. The needle is dipped into the vaccine, then jabbed gently and repeatedly into the patient's arm, just far enough under the skin so the live smallpox virus will "catch."

The bifurcated needle stops entering the body at the point where the prongs meet and prevents the vaccine from being injected too far.

"You want just a tiny bit of blood to come back so you know the skin has been pricked," Collins said.

The unusual application is what requires massive retraining. Nurses practice using a saline solution in place of the vaccine and often use oranges instead of human arms.

"You're used to doing one with a needle and syringe," Collins said, "not 15 times with a bifurcated needle." Nurses are also accustomed to cleaning the area of an injection with rubbing alcohol before administering most vaccines, but alcohol kills the smallpox vaccine.

"As long as the arm is clean, you don't do anything else to clean the arm," Goodfriend said. "If the arm looks dirty, you clean it off with soap and water."

Goodfriend said it is easy to tell whether the vaccine has worked. "With this, because it actually forms a scab on the skin, we'll know they're actually immune to smallpox," he said.

That scab must be covered by a bandage because patients could touch it and spread the virus to other parts of their bodies or to others. The scab takes 21 days to fall off.

But the scab is better than smallpox, which starts with a high fever and other flu-like symptoms before a rash covers the body. The rash forms scabs and leaves ugly scars, if the patient lives. During past outbreaks, one-third of those with the disease died, and there is still no cure.

"It's called an overwhelming infection," Goodfriend said. "Your body can't fight it off. For most people, what will wind up killing them is it will affect your ability to breathe."

The public will not have immediate access to the smallpox vaccine, although there are plans to offer it on a voluntary basis at some point.

"Since there are no cases of smallpox in the world at this time, the possibility of having an adverse reaction to the vaccine outweighs the risk of you getting the disease," Collins said. "If there was a case, all that goes out of the window."

Smallpox last occurred in the United States in 1949 and in the world in 1972. Stores of the vaccine exist in government laboratories around the world.

Public health workers will receive vaccinations and learn how to administer them because officials hope to build capacity to contain any outbreak. If given within three to four days of exposure, Collins said, the vaccine can prevent onset of smallpox.

"It's kind of like knowing how to rescue somebody who's drowning," Collins said of the vaccination training. "You hope you never have to do it."

The nurses Collins will train -- and the nurses they, in turn, will train -- will vaccinate people who would be the first to see a case of smallpox, such as emergency room personnel, emergency medical technicians and police.

The nurses themselves will receive the vaccine. If a case of smallpox were to occur, they would immediately vaccinate people surrounding that patient, moving farther and farther from the direct region of exposure.

Loudoun County public health nurse Gloria Collins, left, demonstrates the smallpox vaccination procedure on Penelope Myer, another nurse.