Researchers have found that while a fresh inoculation may offer the best defense against smallpox, even immunization that occurred 35 years ago or longer retains most of its potency. They report their findings in a letter appearing in tomorrow's issue of The New England Journal of Medicine.
The durability of the vaccine has been a wild card for health officials, who are considering a return to widespread smallpox vaccination to blunt a possible terrorist strike with the microbe. The United States abandoned routine immunization against the virus in 1972, and the World Health Organization declared the infection eradicated in 1980. However, the United States and Russia have preserved samples of the virus, and intelligence experts fear that rogue states like Iraq and North Korea may have obtained supplies of it to use as a bioweapon.
To meet that threat, the Bush administration has set about stockpiling enough smallpox vaccine to cover every American.
Earlier this year, an advisory panel for the Centers for Disease Control and Prevention (CDC) recommended that mass vaccination wasn't necessary and could lead to hundreds of deaths from complications of the inoculation, which involves scratching the vaccinia virus underneath the skin with a tiny pitchfork-like device.
Instead, the group's guidelines produced an estimate that roughly 15,000 health and emergency workers first to respond to a smallpox outbreak might need the vaccine most. Yet, some officials reportedly are urging that as many as half a million people receive it.
The government has yet to announce its decision regarding the panel's recommendations. Bill Pierce, a spokesman for the Department of Health and Human Services, which oversees the CDC, said his agency had given itself a deadline of the end of September to determine its course.
"We're still in the time frame we said we'd be in," he said.
In the new study, which fell out of an HIV experiment, University of North Carolina immunologist Jeffrey Frelinger and a colleague looked at the durability of the smallpox vaccine in 13 lab workers who handle the inoculation.
Of those, four were immunized not more than five years ago, while nine received the vaccine six to 35 years ago and longer. Looking at the response of immune agents called CD8 cells to the vaccinia virus, the researchers saw that people who were immunized recently tended to have the strongest reaction to the vaccine. Yet, those vaccinated more than 35 years ago had only about a third less reactivity, on average, than the recent recipients.
"That's actually pretty resilient to [a virus] you haven't been exposed to for 30 years," said Frelinger, who bared his arm for the study as a volunteer.
Frelinger said policy makers may want to consider his results in prioritizing how smallpox vaccine is distributed, should that prove necessary. "You would want to vaccinate unvaccinated people first," he said.
The study also may be of some comfort to those who've already had at least one round of smallpox vaccine in the past, he added, since their risk of an adverse reaction to the inoculation likely is lower than that of someone naive to it.
What To Do
For more on the various bioterror weapons, try the American Medical Association.