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http://www.nytimes.com/2002/12/10/opinion/10TUE4.html?tntemail0

Guessing How Quickly a Terrorist Smallpox Virus Could Spread

By PHILIP M. BOFFEY

hen President Bush reveals his plan for protecting the nation against smallpox, possibly as early as this week, people will be trying to imagine what might happen if terrorists or a rogue nation like Iraq or North Korea unleashed the disease in this country. Would the virus spread like wildfire, or would it infect only those in very close contact with the initial victims, thus making it easy to snuff out through quarantines and prompt vaccination?

Perhaps the most dramatic example of rapid spread, described in hair-raising detail by Richard Preston in his latest book, "The Demon in the Freezer," occurred at a hospital in Germany in 1970. A smallpox patient who was put in an isolation room somehow managed to infect 17 others in the hospital who had never been in close contact with him. Some were in rooms two floors above him, and one was a visitor who had barely peeked through a hallway door. Investigators concluded that the virus exhaled by the patient's coughing had followed air currents to higher floors either through open windows or through interior halls and stairways.

This was a gripping example of how smallpox, which is usually transmitted in face-to-face contact, can sometimes strike at a distance through the air. But it was a rare case — the patient had severe bronchitis that caused him to cough out germs in copious quantities, and the design and humidity of the hospital were particularly conducive to spreading the virus.

Still, there have been other alarming incidents. In Yugoslavia, a Muslim cleric became infected during a pilgrimage to Iraq in 1972 and unwittingly spread the virus to 11 others, who in turn spread it to 140 more people before anyone realized that smallpox was present in the country. A nationwide vaccination campaign successfully ended the outbreak, but not before 175 people had been infected and 35 had died.

On the other side of the ledger, there is considerable evidence that naturally occurring smallpox moves through a population much more slowly than measles, chickenpox or influenza. The virus spreads from person to person primarily in droplets expelled by coughing or speaking. Patients are not infectious until the rash appears, or perhaps a bit earlier, when the first severe symptoms strike. By that time they are feeling so lousy, with high fevers and aches and pains, that they stay home in bed, posing a danger only to their families or close friends.

Today's opponents of mass vaccination in advance of any attack cite the successful containment of an outbreak in New York City in 1947. A man who had contracted the disease in Mexico was hospitalized with the virus, and 12 people were ultimately infected. The city managed to vaccinate 6.3 million people in just three weeks. In the end, there were two deaths from the smallpox and three from vaccine reactions.

The official World Health Organization Report on the eradication of smallpox asserts that the disease usually spreads "rather slowly" and that its victims rarely infect even five other people. Health workers can break the cycle of transmission by quarantining the victims and their families and vaccinating those nearby. In India, patients suffering from smallpox, with overt rashes, frequently made long-distance trips by train or bus and seldom infected anyone else.

With this sort of mixed history it's easy to see why the current preparations for bioterrorism are a matter of sharp dispute. But all calculations based on past experience must recognize that today's American population, where almost half the people have not been vaccinated against smallpox and the rest have waning protection, is much more vulnerable. The sophistication and size of any attack, and the weather conditions at the time, would greatly affect the damage. If one assumes that smallpox would be introduced one case at a time, say by a suicidal terrorist putting his smallpox-ravaged body near others, the odds of containing any outbreak would seem to be good.

But if the virus was dispensed in aerosols that could infect hundreds of people at a time, who in turn might each infect 10 or 12 others, and if this happened in several cities at once, the scenarios quickly become nightmarish. Should the virus be genetically engineered to spread easily and to overcome vaccinations, the result could be truly catastrophic. But those are worst-case scenarios that exceed the known capabilities of terrorists and rogue states. Or at least we can continue to hope so.

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