Bioterror policy questioned
Model hints U.S. smallpox defence
policy may be flawed.
10 July 2002
TOM CLARKE
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| A deliberate smallpox
outbreak could require mass vaccination. |
| © SPL |
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A new study claims that the current US strategy for
containing a deliberate release of smallpox could lead to tens
of thousands of unnecessary deaths1.
The policy - to trace, vaccinate and quarantine all those
infected and exposed - would be too little and take too long to
protect a large metropolitan area such as New York. The
technique successfully controlled wild smallpox outbreaks in
cities in the last century.
"Ring vaccination would be a disaster," says mathematical
modeller Edward Kaplan of Yale University in New Haven,
Connecticut, who led the study. Its adoption was "based on
assumption instead of analysis", he says, echoing a view held by
several epidemiologists.
Mass vaccination of the entire US population would be a
better way to combat an attack, he suggests. "We need a policy
that can withstand the worst-case scenario," he says.
Government health officials agree that an outbreak of the
size imagined in Kaplan's study would require a broader
vaccination policy. They say they are preparing for just such an
eventuality.
"If there is an emergency and we need to vaccinate widely, we
need to be ready for it. That's what we're doing," Jerome Hauer
of the US Department of Health and Human Services told The New
York Times earlier this week.
The existing policy was designed to minimize the risks of
vaccinating large numbers of people with vaccinia virus - the
smallpox vaccine. The vaccine can be fatal to a tiny percentage
of healthy people. Immunologically compromised people, such as
transplant patients and those living with AIDS, are particularly
vulnerable. The policy was also framed when there was
insufficient vaccine to treat the entire US population.
The policy's critics say that it would be far easier to trace
those who are at risk from the vaccine than those who may have
been exposed in an attack.
Logistical problem
Kaplan built a model of how smallpox might spread that,
unlike previous models, includes estimates of how quickly
healthcare workers could trace and vaccinate victims. "Logistics
are just as important as the epidemiology," Kaplan says.
Assuming that 1,000 people are infected by an initial
release, the model calculates that within 100 days nearly
300,000 people would be infected and almost 100,000 would die.
If, following the outbreak, the entire US population were
vaccinated immediately, only 525 people would die, the model
predicts.
Although praising Kaplan's approach, Steve Leach, a disease
modeller at the Centre for Applied Microbiology and Research in
Porton Down, UK, cautions that predicting how people would move
around following a smallpox attack is extremely hard.
Like any mathematical model, some of its assumptions might be
rather different in a real outbreak, he points out -
particularly how rapidly the virus spreads from person to
person. Using different parameters could yield a much slower
rate of virus spread, for example.
Debate over the best policy is likely to continue. Fears over
a biological attack on the United States are at an all-time high
as relations between the United States and Iraq become
increasingly tense. Iraq is feared to have equipped itself with
a weaponized version of smallpox, or a related virus. |
