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Can postexposure vaccination against smallpox succeed?
1Virus Reference Division, Central Public Health Laboratory, London, United Kingdom. pmortimer@phls.org.uk
Summary
Post-exposure smallpox vaccination, even when delayed, can prevent or attenuate disease. Prompt vaccination of contacts is crucial for bioterrorism preparedness.
Area of Science:
- Public Health
- Infectious Disease Epidemiology
- Vaccinology
Background:
- Smallpox virus poses a bioterrorism threat.
- Limited immunity in the current population due to waning vaccine effectiveness and lack of widespread primary vaccination since the 1970s.
Purpose of the Study:
- To evaluate the effectiveness of post-exposure smallpox vaccination.
- To inform modern contingency planning for bioterrorist smallpox release.
Main Methods:
- Review of historical data on post-exposure vaccination outcomes.
- Analysis of vaccination timing relative to disease onset and severity.
Main Results:
- Prompt vaccination of smallpox virus contacts often prevented disease entirely.
- Revaccination within the first week of incubation was highly protective.
- Revaccination in the second week attenuated disease and reduced mortality.
- Primary vaccination within 4 days of exposure was generally protective against severe illness.
Conclusions:
- Modern bioterrorism preparedness must include rapid contact tracing and vaccination capabilities.
- Anticipatory vaccination strategies should be considered for populations with low immunity, especially in potential target countries, due to the risk of delayed vaccination reach.