Although naturally occurring smallpox was eradicated in 1977, there is concern that bioterrorists might obtain smallpox from a laboratory and release it into the population.
Under such circumstances, the supply of smallpox vaccine may be insufficient for universal administration. In a study published in the December 2008 issue of The American Journal of Medicine, researchers found that lifetime protection is obtained from just one vaccination, even when that vaccination occurred as much as 88 years ago. They conclude that in the event of a smallpox bioterrorist attack, vaccinia smallpox vaccine should be used first on individuals who have not been vaccinated previously.
Examining 246 participants of the Baltimore Longitudinal Study of Aging, investigators from the National Institute on Aging and the National Institute of Allergy and Infectious Diseases, National Institutes of Health found permanent immunity was conferred by vaccination or by survival from an active smallpox infection. In the sample, 209 subjects were vaccinated one or more times 13 to 88 years prior to the study; an additional 18 had had childhood smallpox, and 29 with no history of vaccination or smallpox were included.
Although the vaccinia virus vaccine was used since the late 18th century, routine vaccination was discontinued more than 30 years ago in many countries. Most Americans under 35 have never been vaccinated and most over 35 have not received booster immunizations since the early 1970s. If a bioterrorist attack were to occur, it would be critical to know who already had effective immunity and would not need to be vaccinated, leaving another dose available for someone else.