The last American to catch smallpox was in 1949 in Hidalgo County at the southern tip of Texas. The last human got the deadly virus on Oct. 26, 1977 in Merca, Somalia.

Now a quarter-century later, President Bush is deciding whether thousands of Americans should get sick, or even die, to protect the nation from the possibility of a terrorist smallpox attack.

If the president OKs a plan to immunize the population as a precaution, scientists said side effects from the smallpox vaccine could kill at least 100 people, send at least 4,000 to the hospital and cause mild to moderate illness in another 100,000.

That scenario is based on the assumption that 100 million of the nation's 280 million people agree to get the voluntary vaccinations, and on the vaccine's track record as one of the riskiest around. Babies under age 1 are most vulnerable.

The issue hits home this week, when county health departments in South Florida and across the state must turn in plans for how they would mount the mass effort to vaccinate the population.

Vice President Dick Cheney tops a list of White House and intelligence officials who favor offering the vaccine to every American soon, based on reports that Iraq and terrorists have smallpox that could be made into a weapon.

The government has revealed little about the immediacy of the threat, but supporters of mass innoculations said the nation cannot afford to wait. Their target date for vaccinations: 2004.

"I think we're nuts not to offer vaccination to the public immediately if we're about to go to war," said Peter B. Jahrling, a smallpox scientist at the Department of Defense.

The U.S. Centers for Disease Control and Prevention had opposed the idea, but now agreed to consider changing course and recommending mass innoculation.

Most medical experts, however, do not favor widespread vaccinations because a smallpox attack seems unlikely, and if it ever came would likely be isolated and containable.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and the American Academy of Pediatrics are two that say there's no need to vaccinate the public on speculation.

"There's only a remote chance of an attack," said Dr. Robert Baltimore, a Yale University pediatrician who is a member of the academy's smallpox committee. "From what we know about the side effects of the vaccine -- the only vaccine we know -- the risks outweigh the benefits."

While Bush weighs his options, the vaccine will be given -- maybe within months -- to an estimated 500,000 military personnel and about 500,000 medical professionals around the county who are designated to treat smallpox victims and coordinate the response in an attack. Next would come "first responders" such as paramedics and police officers.

Florida expects to get 20,000 to 50,000 doses for that first wave of vaccinations. South Florida stands to receive one-third of the vaccine. Local health officials said they could immunize all the health-care workers within a few days.

"We could do it. The details are still up in the air," said Dr. Tammy Blankenship, a former U.S. Navy disease detective who is director of disease prevention and surveillance at the Broward County Health Department.

A `tricky' process

It's not as simple as picking 50 people at every hospital, said the department's medical director, Dr. Robert Self: "This is going to be a very tricky process." The tricky part? Weeding out people who would be most at risk from the vaccine.

Smallpox has killed millions over at least 3,000 years. The virus, variola, can spread rapidly through bodily fluids coughed or sneezed by infected people during prolonged face-to-face contact, through contaminated items, or rarely, through the air. There's no cure.

The virus incubates silently in the body for 7 to 17 days, then breaks out as pustules with high fever, rash, vomiting and fatigue. In the past, the virus killed 30 percent of its victims, with rare forms 100 percent fatal.

Scientist Edward Jenner devised the vaccine in 1796, injecting people with a similar but milder virus, vaccinia, to spur the body's defenses to kill smallpox along with the vaccinia.

Health workers give the vaccine by dipping a two-pronged needle into a solution of live virus, then pricking the shoulder 15 times in a circle about the size of a dime. The virus typically breaks out the area into a sore that lasts two weeks.

"It wasn't painful when you're getting it, but a few days afterward when the scab starts, it itched and it was uncomfortable. It wasn't a fun thing," said Elissa Fabian, an infection control nurse at Holy Cross Hospital in Fort Lauderdale who gave the vaccine during the 1960s.

It worked wonderfully. The vaccine protected more than 97 percent of those who received it. The breakthrough wiped smallpox from the globe over two centuries. The United States immunized babies until deciding in 1972 that the nation was smallpox-free.

But for about 1 per 1,000 people, the vaccine was a danger.

Studies in the 1960s showed that the vaccinia virus killed one or two people per million who received it, the CDC says. Most victims were babies under age one whose defenses were overwhelmed and who often died from encephalitis, a fatal swelling of the brain.

About 40 people per million vaccinations developed life-threatening illnesses, such as encephalitis and serious skin infections including eczema. Another 1,210 per million came down with milder side effects, mainly infections. The CDC says vaccinations should not be given to people with weak immune systems, pregnant women, babies under age 1 and those with skin conditions unless they are directly exposed to smallpox.

Some experts think the population's risk is higher now, because many more people have immune problems from HIV/AIDS and from taking immune suppressant drugs for cancer. Also, eczema has doubled in recent decades for unclear reasons.

Health officials also worry because vaccinated people occasionally have spread the vaccinia virus to their children, parents or close contacts, via secretions from a sloppily covered vaccine sore. This weighs heavily on hospital workers who would be the first immunized.

"I think most of those we have designated to get it are willing to do so. But they are already asking questions. They want to know the risks to their families," said Fabian, a smallpox planner at Holy Cross.

Some health officials say the president should hold off vaccinating the entire population until seeing the results of immunizing the military and health workers.

"Give it to a small number of people and then learn from it," said Dr. Savita Kumar, director of epidemogy and disease control at the Palm Beach County Health Department.

If an attack came before a mass vaccination, the Bush administration wants to innoculate the entire population within two weeks, before the virus becomes contagious and while the vaccine still has the power to thwart it.

"I think it would be optimistic to vaccinate millions of people in 10 days," Kumar said. "It is achievable, I guess."

South Florida's plan

What would it be like in South Florida?

Since very few people today know how to give the vaccine, county health departments plan to draft and train public health nurses and volunteers from the medical community such as paramedics and retired nurses.

They envision people lining up for shots at schools, shopping malls, churches, community centers and government buildings, Kumar said. To immunize a million people in 10 days, the CDC says it would take 20 locations with eight vaccine stations apiece working 16 hours a day, with 230 workers for each location.

Local officials are not sure how quickly they could mobilize such a large operation. They hope it would take no more than a day. In an attack area, the government could halt all transportation and quarantine people to contain the virus.

Bush is contemplating a voluntary vaccination plan, so every family will have to decide whether to take a chance on it.

"You have to weigh what are the odds of a bioterrorist attack and what are the odds it would be smallpox, against the risk of the vaccine," said Blankenship, of the Broward health department.

"I myself would have no problem being the first in line," she said. "If you're a parent and you could protect your child with a vaccine, I guess they would want to."

Kumar in Palm Beach County disagrees: "Everyone at this point does not need the shots. The risk is much higher than the benefit from giving everyone the vaccine."

About 55 percent of Americans were already vaccinated before 1972, but a report from the American Society of Health-System Pharmacists said little of that protection remains today.

Those who vaccinated long ago likely would not get sick if they were innoculated again, Blankenship said.

Many health officials favor vaccinating only relatives, co-workers, schoolmates and people who had extended, direct contact with the victims of a smallpox attack. The so-called ring theory aims to isolate those infected and to bottle the virus within a ring of vaccinated people.

"If you get one or two cases, it will cause a lot of panic in the county, but will be real easy [to contain] from the public health end of it," Broward's Self said.

One study showed that the ring approach would result in fewer illnesses than mass vaccination if the initial attack infected fewer than 1,000 people, but that mass vaccinations would protect better in a larger attack.

Some smallpox experts dispute conventional wisdom that the virus would spread rapidly. They contend the virus rarely spreads unless a person has six hours of continuous close contact with an infected person, which is unusual in schools or among co-workers in the next cubicle. That bolsters the ring approach.

Such questions are key for those deciding if the nation has enough vaccine.

15 million doses

The CDC has about 15 million doses of freeze-dried vaccine, Dryvax, made before 1972. Manufacturer Aventis-Pasteur recently turned over another 75 million doses found in its freezer. Studies show those could be diluted 5 to 1 and still protect, so there's enough to cover the population.

The government also is paying $770 million to the Acambis PLC and Baxter International to make 209 million new doses, due by Dec. 31. Bush would prefer to wait for the new batch to vaccinate the public.

Another big decision for Bush is whether to let the National Institutes of Health test the vaccine on preschoolers, to make sure it is effective. The proposal is to innoculate 40 children ages 2 to 5 in Los Angeles and Cincinnati.

Bad idea, says the Alliance for Human Research Protection. Why risk making babies seriously ill when there's only a tiny chance anyone would be exposed, asks David Cohen, a social work professor at Florida International University who is a member of the group's board.

But the NIH has persuaded even some mass-vaccination opponents that the risk is tiny enough that tests should be done before an attack.

"[An attack] would be a bad time to find out there were problems with the vaccine in terms of children not responding or having unforeseen problems from the vaccine," Baltimore said.

Bob LaMendola can be reached at blamendola@sun-sentinel.com or 954-356-4526.