Smallpox: Risks, Vaccination, and Potential Outcomes

1. Why Smallpox Bioterrorism? • Stable aerosol Virus • Easy to Produce • Infectious at low doses • Human to human transmission • 10 to 12 day incubation period • High mortality rate (30%) • CDC Materials

2. Small Pox Vaccine History • 1000 AD - China, deliberate inoculation of smallpox into skin or nares resulting in less severe smallpox infection. Vaccinees could still transmit smallpox • 1796 - Edward Jenner demonstrated that skin inoculation of cowpox virus provided protection against smallpox infection • 1805 - Italy, first use of smallpox vaccine manufactured on calf flank • 1864 - Widespread recognition of utility of calf flank smallpox vaccine • 1940’s - Development of commercial process for freeze-dried vaccine production (Collier)

3. Herd Immunity • Smallpox Spreads to the Non-immune • Immunization Slows the Spread Dramatically • Epidemics Die Out Naturally • Herd Immunity Protects the Unimmunized

4. Smallpox Vaccine • Live Virus Vaccine (Vaccinia Virus) • Not Cowpox, Might be Extinct Horsepox • Must be Infected to be Immune • Crude Preparation We Have Now • Prepared from the skin of infected calves • Filtered, Cleaned (some), and Freeze-dried • New Vaccine is Clean, but still Live

5. Complications of Vaccination • Local Lesion • Can be Spread on the Body and to Others • Progressive (Disseminated) Vaccina • Deadly Like Smallpox, but Less Contagious • Encephalitis • Heart Disease?

6. Historic Probability of Injury • Small Risk from Bacterial and Viral Contaminants • Small Risk of Allergic Reaction • 35 Years Ago • 5.6M New and 8.6M Revaccinations a Year • 9 deaths, 12 encephalitis/30-40% permanent • Death or Severe Permanent Injury - 1/1,000,000 • Mostly among immunsupressed persons

7. Global Eradication Program • 1950 - Pan American Sanitary Organization initiated hemisphere-wide eradication program • 1967 - Following USSR proposal (1958) WHO initiated Global Eradication Program • Based on Ring Immunization • Vaccinate All Contacts and their Contacts • Isolate Contacts for Incubation Period • Involuntary - Ignore Revisionist History • 1977 - Oct. 26, 1977 last known naturally occurring smallpox case recorded in Somalia • 1980 - WHO announced world-wide eradication

9. Eradication Ended Vaccinations • Cost Benefit Analysis • Vaccine was Very Cheap • Program Administration was Expensive • Risks of Vaccine Were Seen as Outweighing Benefits • Stopped in the 1970s • Immunity Declines with Time

10. Universal Vulnerability • Agriculture and Smallpox • Stays Endemic or Dies Out Forever • Most Communities had Significant Immunity • Isolated Communities • Synchronous Infection • Break Down of Social Order • Now the Whole World is Susceptible

11. How Have Risks Changed? • Immunosuppressed Persons Cannot Fight the Virus and Develop Progressive Vaccinia • Immunosuppression Was Rare in 1970 • Immunosuppression is More Common • HIV, Cancer Chemotherapy, Arthritis Drugs, Organ Transplants

12. Role of Medical Care • Smallpox • Can Reduce Mortality with Medical Care • Huge Risk of Spreading Infection to Others • Very Sick Patients - Lots of Resources • Cannot Treat Mass Casualties • Vaccinia • VIG - more will have to be made • Less sick patients - longer time

13. Complications Last time - 1947 New York Outbreak • Case from Mexico • 6,300,000 Vaccinated in a Month • 3 Deaths from the Smallpox • 6 Deaths from the Vaccine • Would Have Been Much Higher Without Vaccination?

14. What would happen now? • Assume 1,000,000 Vaccinated in Mass Campaign with No Screening • Assume 1.0% Immunosuppressed • 10,000 Immunosuppressed Persons • Probably Low, Could be 2%+ • Potentially 1-2,000+ Deaths and More With Severe Illness