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Immunity from Smallpox Vaccine Persists for Decades: A Longitudinal Study

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.


The threat of smallpox resulting from bioterrorist action has prompted a reassessment of the level of immunity in current populations.

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.

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.

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.

3 Responses to “Immunity from Smallpox Vaccine Persists for Decades: A Longitudinal Study”

  1. I was really very happy to see that smallpox vaccine has a very long protective effect as noted in this article. This means that a fair amount of smallpox herd immunity exists in our current western population since most of us were vaccinated as children. Joseph Alpert

  2. Thanks for the information on smallpox. It’s great to know the vaccine lasts longer than originally thought!

    We recently wrote an article on smallpox vaccines at Brain Blogger. Recently, people have had a renewed interest in creating new smallpox vaccines in order to fight the smallpox pathogen being used as a bioterrorism weapon. But smallpox was once all but eliminated from existence until resent years; what are are chances of making a new vaccine that will be more effective?

    We would like to read your comments on our article. Thank you.


  3. Dear K: I read your article on smallpox vaccination and agree with everything that you stated. We all hope that the small amount of residual smallpox vaccine is closely guarded and cannot be stolen for terrorist or war time use. However, it makes good preventive sense to prepare new vaccines for smallpox, perhaps ones that are even safer than the old vaccine which occasionally caused some problems such as disseminated vaccinia and perimyocarditis. Joseph Alpert, editor, AJM