Staying Home Could Contain Smallpox Attack

Mass vaccinations not needed in outbreak, concludes study

WEDNESDAY, May 12, 2004 (HealthDayNews) -- What would you do if you learned terrorists had unleashed smallpox on your city or town? The best advice, say government experts, is to sit tight.

In a letter in the May 13 issue of Nature, researchers from the Los Alamos National Laboratory conclude that mass vaccination probably isn't necessary in the event of a bioterrorism attack with smallpox. Instead, they say, if everyone with a fever simply stayed home, a large-scale smallpox outbreak could be averted.

"Things aren't as dire as they might seem," said study author Stephen Eubank, team leader for the urban infrastructure simulation suite at the lab, based in Los Alamos, N.M. "It looks as though the best response to a smallpox attack would be to encourage people who are sick to stay home. Anybody with a fever should stay home. That simple statement could capture all of the people who were infectious," he said.

Smallpox is a contagious and potentially fatal infectious disease. The last naturally occurring case happened in Somalia in 1977. There hasn't been a case of smallpox in the United States since 1949, according to the U.S. Centers for Disease Control and Prevention.

While the disease is contagious, it's not as easily spread as some other diseases. Smallpox requires more than casual contact to pass the disease from one person to another. The transmission of smallpox usually requires prolonged, direct contact with an infected person or an object that an infected person has contaminated.

People with smallpox are most infectious when they break out in the smallpox rash, according to the CDC, but they can also be contagious earlier, when running a fever.

Using a simulation tool dubbed EpiSims that combines population models with information on the transmission of disease, the researchers were able to develop a realistic model of an urban setting undergoing a biological attack with smallpox. The population data was based on Portland, Ore.

The model created a synthetic population that can estimate the positions and activities of all of the people in the city on a second-by-second basis.

For their simulated attack, the researchers assumed the smallpox would be distributed indoors over several hours in busy locations, directly infecting about 1,000 people. The researchers also assumed that smallpox wasn't detected until 10 days after the attack.

Based on their model, Eubank and his colleagues feel there may be no need for mass vaccinations in the unlikely event of a smallpox attack. Quick detection of the disease and targeted vaccination of at-risk people, along with keeping them away from others, would probably contain a smallpox outbreak.

Dr. Elizabeth Halloran, from the department of biostatistics at the Rollins School of Public Health at Emory University, said this model confirms the results of other studies and this model is particularly interesting because it's based on actual survey data from Portland.

"The message is don't panic. It's not that easy to spread smallpox through the population if you're taking appropriate measures. Proper preparedness would prevent the spreading of disease," she said.

She added that smallpox doesn't spread quickly like SARS or flu: "Smallpox moves very slowly and has a long incubation period. It can be contained."

More information

To learn more about smallpox, visit the U.S. Centers for Disease Control and Protection. And here's more information from the CDC on what is being done to prepare in case of a bioterrorism attack with smallpox.

SOURCES: Stephen Eubank, Ph.D., team leader, urban infrastructure simulation suite, Los Alamos National Laboratory, Los Alamos, N.M.; Elizabeth Halloran, M.D., D.Sc., M.P.H., department of biostatistics, Rollins School of Public Health, Emory University, Atlanta; May 13, 2004, Nature
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