Routine smallpox vaccination was discontinued over 30 years ago, following world-wide eradication of the virus. Potential re-emergence of this disease from bioterrorist action has prompted international health care authorities to reassess the level of immunity in current populations. This study found that immunity from smallpox vaccination lasts for decades.
Abstract
Background
The threat of smallpox resulting from bioterrorist action has prompted a reassessment of the level of immunity in current populations.
Methods
We have examined the magnitude and duration of antiviral antibody immunity conferred by smallpox vaccination in 246 participants of the Baltimore Longitudinal Study of Aging. Of this population, 209 subjects were vaccinated one or more times 13 to 88 years before this evaluation, and stored serum samples were available at various intervals after vaccination. An additional 8 subjects who had documented childhood smallpox infection and 29 subjects with no history of infection or vaccination were included. We quantified the total vaccinia IgG and neutralizing antibody titers in each of these subgroups of participants over time.
Results
Vaccinated participants maintained antivaccinia IgG and neutralizing antibody titers above 3 natural logs essentially indefinitely. The absolute titer of antivaccinia antibody was only slightly higher after multiple vaccinations. In 97% of the participants, no decrease in vaccinia-specific antibody titers was noted with age over a follow-up period of up to 88 years. Moreover, Baltimore Longitudinal Study of Aging participants who survived active smallpox infections in their youth retained antivaccinia antibody titers that were similar to the levels detected in vaccinated subjects.
Conclusion
These data suggest that multiple or recent vaccinations are not essential to maintain vaccinia-specific antibody responses in human subjects. Scarce vaccine supplies should be applied first to individuals who have not previously been vaccinated.
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– Dennis D. Taub, PhD, William B. Ershler, MD, Mark Janowski, MD, Andrew Artz, MD, Michael L. Key, Julie McKelvey, Denis Muller, MS, Bernard Moss, MD, PhD, Luigi Ferrucci, MD, PhD, Patricia L. Duffey, Dan L. Longo, MD
This article was originally published in the December 2008 issue of The American Journal of Medicine.
