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Expected adverse events in a mass smallpox vaccination campaign
Alex R Kemper1, Matthew M Davis, Gary L Freed
1Division of General Pediatrics, University of Michigan, Ann Arbor, USA. kempera@med.umich.edu
Effective Clinical Practice : ECP
|May 7, 2002
Summary
Mass smallpox vaccination could lead to significant adverse events and deaths, especially in older populations. Careful exclusion of high-risk individuals is crucial to mitigate these risks.
Area of Science:
- Public Health
- Epidemiology
- Vaccinology
Background:
- Recent anthrax attacks heightened concerns about bioterrorism preparedness, including vulnerability to smallpox.
- Strategies for mitigating smallpox attack impact include quarantine, contact vaccination, and routine vaccination resumption.
Purpose of the Study:
- To assess the likely consequences of mass smallpox vaccination, including adverse events and mortality.
- To inform decisions regarding the resumption of routine smallpox vaccination.
Main Methods:
- Calculated the number of adverse events based on incidence rates and estimated vaccine uptake (75%) from historical data.
- Excluded high-risk individuals (e.g., those with eczema, immunocompromised) and their close contacts from vaccination estimates.
- Utilized January 2000 U.S. Census data for population estimates.
Main Results:
- Common adverse events include fever (<1 in 5) and rash (<1 in 100).
- Serious adverse events like encephalitis (<3 in 1 million) and death (<2 in 1 million) are more common than with other vaccines.
- Vaccinating 1-29 year olds (excluding high-risk) estimates 1600 serious events and 190 deaths; vaccinating 1-65 year olds estimates 4600 serious events and 285 deaths.
Conclusions:
- Smallpox vaccine has a higher complication rate than other currently used vaccines.
- Careful exclusion of high-risk individuals is essential but leaves some population susceptible.
- The decision to resume vaccination requires weighing smallpox attack risks against mass immunization harms.