Study Predicts Impact of Smallpox Attack

Surprise Finding: Mass Vaccination Not Worth it

From the WebMD Archives

Dec. 19, 2002 -- More than 40,000 people would die if there were a large-scale smallpox bioterror attack on an airport, researchers calculate.

It's a horrible thing to think about. But that worst-case scenario must be considered in the debate over whether it's a good idea to vaccinate everyone against smallpox. What are the real risks from smallpox? That's the focus of several reports in an extraordinary early release from the Jan. 30, 2003, issue of TheNew England Journal of Medicine.

The most provocative of these reports is a calculation of the risks from various smallpox-attack scenarios. Samuel A. Bozzette, MD, PhD, and colleagues at RAND Health Care and the VA San Diego Healthcare System pose a number of "what if" scenarios. These range from an accidental laboratory release to a major bioterror attack on a large airport.

The surprising finding: Even a worst-case scenario doesn't justify mass public vaccination before there is an attack.

"Our study shows that in order for there to be a substantial advantage for mass vaccination of the public, we would need to be facing a significant threat of a very widespread attack," Bozzette tells WebMD. "This is because the conventional methods of containment -- vaccination of contacts and isolation of the ill -- work reasonably well. If we were to vaccinate the public, thousands would become ill and 500 or so people would die."

If only healthcare workers were vaccinated before a large-scale attack, about 43,000 people would die. Prior mass vaccination would cut this to about 13,000 deaths. But the cost of preventing those "what if" deaths would be the 500 very real vaccine-related deaths.

"The main issues are that smallpox isn't an instant killer, and that there is a lot of vaccine on hand," Bozzette tells WebMD. "If there is an attack, there will be time to carry out a widespread vaccination program. This should reassure people."

Despite this reassurance, the calculations show that mass public vaccination after an attack would not do a lot of good. However, the study does show that advance vaccination of healthcare workers is worthwhile. That's because healthcare workers run a much higher risk of infection.


"Basically, there will be harm associated with distribution of the vaccine," Bozzette says. "Healthcare workers are only 3% of the population, but in our study, we would predict they would be 20%-60% of all the cases. Moreover, healthcare workers need to stay healthy and confident they are protected in order to operate the health system for all of us. So since there is greater risk, the benefit threshold is lower for vaccination of healthcare workers. And because they are so many fewer in number, the number harmed is much smaller. We estimate 25 deaths -- which is still not nothing."

So would Bozzette get the smallpox vaccine? What about his family?

"I think we can look to the example of what the president is doing with his family as what an informed judgment might look like," Bozzette says. "I am an infectious-disease specialist; I am going to be vaccinated. My wife is a pathologist; she is going to be vaccinated. But my children, my parents, my sisters, and their children are not going to be vaccinated. Our family knows they are not helping the nation by getting vaccinated. They understand that even if there is an outbreak they are not likely to be infected and that there will be time to get vaccinated."

A smallpox attack on an unvaccinated U.S. public would be "catastrophic," said D.A. Henderson, MD, MPH, Johns Hopkins University distinguished service professor and senior science advisor to the secretary of Health and Human Services, an a previous interview. Henderson's standing -- he was a leading force in world smallpox eradication -- convinces some bioterror experts that a smallpox attack is a worst-case scenario.

Others are not so sure. One is Kent A. Sepkowitz, MD, director of infection control at Memorial Sloan Kettering Cancer Center and associate professor of medicine at Weill Medical College, Cornel University, New York.

"Remember Y2K. This is a comparable non-event," Sepkowitz tells WebMD.

Another is Thomas Mack, MD, MPH, professor of preventive medicine, Keck School of Medicine, University of Southern California, Los Angeles. Like Henderson, Mack is a veteran of the world war on smallpox. He led teams that investigated some 100 smallpox outbreaks. His NEJM editorial argues that smallpox is overrated as a bioterror weapon.


"A smallpox attack is not a worst-case bioterror scenario," Mack tells WebMD. "People greatly exaggerate the danger to the population not directly affected. They picture smallpox being transmitted like wildfire, and that doesn't actually happen. It is more like a grenade than like a dirty bomb. Once the initial wave of infections is over, mopping up is relatively simple."

Unlike many other diseases, people with smallpox can't infect other people until they start to feel ill -- a couple of weeks after infection. And if people know they've been exposed, getting vaccinated within a few days can keep them from getting sick. Both these facts mean health workers have time to stop a smallpox epidemic before it gets out of hand.

"Suppose the worst case: the aerosolization of live smallpox virus applied to a substantial population, say into a shopping center," Mack says. "Maybe if there was some way to keep it in the air, then, yes, under very extreme circumstances you could infect a large number of people. But the average number of people they infect is not going to change [from what we've seen in natural epidemics]. They don't get smallpox from weaponized virus any more, but from somebody's mouth. If they are put in hospitals, they will be dangerous. But once a first case appears, every community will find a place to put people away from the general hospital population."

One of the most striking NEJM papers is a survey of what Americans know -- and, mostly, don't know -- about smallpox and smallpox vaccination. Robert J. Blendon, ScD, professor of health policy and political analysis Harvard School of Public Health, and colleagues conducted telephone interviews with a national sample of 1,006 adults.

Among the striking findings:

  • 84% of Americans don't know that right now there is enough smallpox vaccine to vaccinate everyone in the U.S. in the event of a smallpox attack.
  • 63% of Americans think there's been a case of smallpox somewhere in the world in the last five years. And 30% think there's been a recent case of smallpox in the U.S. The reality: There hasn't been a case of smallpox since 1977 -- anywhere.
  • 78% of Americans think there is an effective treatment for smallpox. The reality: There is no such treatment.
  • 58% of Americans don't know that vaccination within a few days of smallpox exposure can prevent disease.
  • 73% of Americans say they'd get smallpox vaccination if their own doctor and most other doctors were vaccinated. However, this number fell to just 21% if their own doctor and many other doctors refused vaccination.


Smallpox Vaccine Risks

What will happen if lots of people start getting vaccines based on decades-old technology? The answer: Many people will suffer side effects, and some -- an estimated one to five in a million -- will die.

But there's good news. One of the most feared side effects of public vaccination is the accidental spread of the live-virus vaccine from a vaccinated person to an unvaccinated person. People with damaged immune systems -- such as transplant recipients, people taking immune-suppressing treatment for arthritis and other conditions, cancer patients on chemotherapy, and AIDS patients -- are at enormous risk of vaccine complications.

Are these people at risk from vaccinated people? Not much, according to the NEJM report from Sepkowitz. The Weill Medical College professor took a careful look at all the medical literature on the topic.

"The vaccine virus is very uncontagious," Sepkowitz tells WebMD. "It would take the wrong person being in the wrong place at the wrong time -- and a [break with] standard infection control practices in hospitals for a person to get secondary disease. The risk will be small but not zero."

Mack, however, argues against mass public vaccination.

"This is the most dangerous live vaccine we have," he says. "It is going to kill people. It may be just a few people in a million, but it still will kill people. Overall, vaccinating people in general is not cost effective. It will hurt more people than it helps. I think even vaccinating people who work in hospitals is not effective. We will hurt more people than we save. If someone showed me evidence that someone is planning sustained multiple attacks, I would change my mind."

Eventually, smallpox vaccination will be available for all Americans. The decision on whether to get vaccinated is personal. There is a risk. Is the benefit worth the risk? Most of the experts who spoke with WebMD agree with Blendon: Ask your doctor.

"Decisions are best made on a rational, factual basis and not on the basis of fear," Edward W. Campion, MD, NEJM senior deputy editor, tells WebMD. "Physicians do have a major role. If there is going to be any type of widespread vaccination, patients are going to be coming to doctors to ask, 'Should I be vaccinated or not? What is your opinion?'"


This makes it more important than ever for doctors to be informed -- and to be aware that they are role models.

"At this moment I am making the decision as frontline person to get vaccinated, but I am not having my family vaccinated," Blendon says. "That is important for people to know. It is more important for patients to know what their doctor says than what a cabinet secretary says. Physicians are critical. People are going to be watching what they say."

WebMD Health News Reviewed by Michael W. Smith, MD on December 19, 2002


SOURCES: The New England Journal of Medicine, Jan. 30, 2003 • Samuel A. Bozzette, MD, PhD, RAND Health Care and VA San Diego Healthcare System • Robert J. Blendon, ScD, professor of health policy and political analysis, Harvard School of Public Health • Edward W. Campion, MD, senior deputy editor, NEJM • Kent A. Sepkowitz, MD, director of infection control, Memorial Sloan Kettering Cancer Center; and associate professor of medicine at Weill Medical College, Cornel University, New York • Thomas Mack, MD, MPH, professor of preventive medicine, Keck School of Medicine, University of Southern California, Los Angeles • D.A. Henderson, MD, MPH, Johns Hopkins University distinguished service professor; and senior science advisor to the secretary of Health and Human Services.

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