- While many Americans worry that bioterrorists will strike
with smallpox before the USA has enough vaccine, studies suggest that
people
immunized 50 years ago or more still have some protection. Researchers
also say mass immunization probably wouldn't be necessary because smallpox
is not as contagious as other bugs such as measles or the flu. "It's
not going to be the Armageddon that some would have you believe,"
says smallpox expert James LeDuc of the Centers for Disease Control and
Prevention. In some countries, smallpox was eradicated after less than
two-thirds of people were immunized, LeDuc says.
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- When it comes to smallpox vaccine, the immune system
appears to have a long memory. "Even if you're over 50 years old and
saw the vaccine when you were a child, the risk of dying from infection
is much less than if you've never seen the vaccine," LeDuc
says.
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- The United States stopped giving smallpox vaccinations
in 1972, but the government wants to stockpile doses in case of an
attack.
-
- LeDuc says the CDC this month will rewrite a section
of its Web site to better explain the issue of residual immunity.
Currently,
the Web site states that smallpox vaccine protects for only three to five
years.
-
- A 1913 report about a 1902-03 outbreak in Liverpool,
England, provides the earliest clues about the vaccine's legs. The study
analyzed the severity of disease in 1,163 people.
-
- There were 55 cases among people 50 and older who had
been vaccinated in their childhood. Only four were severe, and only three
died, says Frank Fenner, co-author of Smallpox and Its Eradication and
researcher at the John Curtin School of Medical Research in Canberra,
Australia.
By comparison, Fenner says, the disease killed six of the 12 victims 50
and older who had never been vaccinated.
-
- In 1996, scientists from the University of Massachusetts
Medical Center in Worcester reported that immune cells from healthy
volunteers
recognized the vaccinia virus " used to immunize against smallpox
" as a foe. Yet up to 50 years had passed since the volunteers'
smallpox
vaccinations.
-
- It's not clear how the immune response seen in the lab
would translate into real life, says study co-author Francis Ennis. While
immunity persists for decades, Ennis says, it most likely does wane over
time.
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