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Study Predicts Impact of Smallpox Attack

Surprise Finding: Mass Vaccination Not Worth it
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WebMD Health News

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."

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