http://abcnews.go.com/wire/US/reuters20021114_473.html
Targeted Smallpox Shots Could Be Enough, Study Says
Nov. 14
— By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - It may not be necessary to vaccinate the entire population against smallpox in case there is ever a biological attack, U.S. researchers said on Thursday.
If people vaccinated before 1972, when the United States stopped the practice, have some remaining protection against the disease, they would act as a barrier to help slow the spread of any epidemic, the team at Emory University found.
"If people vaccinated before 1972 have about 50 percent residual immunity, then a targeted vaccination strategy works about as well as mass vaccination," Dr. Elizabeth Halloran, an expert in making computer models of infectious disease outbreaks, said in a telephone interview.
"If there is no residual protection, then mass vaccination works better."
Smallpox was eradicated as a disease in 1978 and the United States stopped vaccinating people in 1972. But with recent fears of a bioterrorist attack, U.S. officials have been considering whether to vaccinate at least some of the population.
Vaccination advisers to the U.S. government have recommended immunizing about 500,000 "first responders" and emergency workers so they could help without endangering themselves. President Bush has recommendations in hand but has not decided what to do.
No one is sure how many of those vaccinated before 1972 are still immune. Most experts say they believe people may be protected from the most deadly effects of the virus, which, when it was rampant, killed about 30 percent of victims.
Those who were vaccinated may also be less likely to spread it.
Halloran and colleagues ran a series of computer models based on several scenarios. They ran the models twice -- once assuming that everyone vaccinated before 1972 had no protection left, and then assuming they had about 50 percent of full protection left.
Writing in the journal Science, they said it could be more effective to vaccinate just people likely to have had close contact with victims.
"Our model, the community structure, was based loosely on the U.S. census," Halloran said. "It includes households, schools, a community of 2,000."
They assumed that people can pass on the disease for the three to five days during which they feel ill but before they develop the distinctive pustules, the pox, that makes the disease so disfiguring.
"During the flulike period there is a lot more virus in the throat than later," said Halloran, who is also a medical doctor. "For that reason we decided that this period of the flulike symptoms ... that it's more infectious than after the pox starts."
They also used real-life experience with smallpox outbreaks as the basis for assuming that smallpox is more likely to be transmitted through close contact, such as in a household, than through casual contact on the streets or on a commuter train.
In 2001 the U.S. government ordered millions of doses of smallpox vaccine and now says it has enough, in the words of Health and Human Services Secretary Tommy Thompson, to vaccinate "every man, woman and child" in the country.
