Although smallpox was eradicated in 1977, the possibility of a bioterrorist attack with the deadly virus has health officials worried. But a new study reports that should the virus re-emerge, those who had previously been vaccinated would largely be immune to the disease.
Researchers analyzed 50 years of blood chemistry data from 246 participants in the ongoing Baltimore Longitudinal Study on Aging and looked at various samples for the same individual over time to check his or her immune response.  

Dennis Taub is acting chief of the laboratory of immunology at the National Institute on Aging and lead author of the report, published in the December issue of The American Journal of Medicine. He says 97 percent of the participants studied retained immunity to smallpox.

"That means that they actually retained a level of antibody that was measurable and, based on the literature, was deemed to be protective," Taub says.

Immunity remained high without booster shots, even for those participants in their 80s and 90s. Taub says the findings can help public officials better distribute vaccines in the event of an attack.

"If you have limited supplies, they might be more usefully applied to people who have never been exposed than those who have been vaccinated," he says.

The supplies would be targeted at people born after 1972, when vaccination against smallpox was terminated.