Smallpox: History, Global Impact, and Eradication

Deadliest Infectious Disease in Human History

Smallpox (variola virus) caused an estimated 300–500 million deaths in the 20th century alone—more than all wars combined.

Disease Characteristics

• Highly contagious (R₀ 3.5–6); respiratory droplet/spread.
• Incubation 7–17 days; then high fever, prostration, centrifugal rash (macules → papules → vesicles → pustules → scabs).
• Case fatality: 30% (variola major); <1% (variola minor).
• Survivors: permanent scarring, blindness, limb deformities.

Eradication Triumph

• 1959: WHO launches global eradication program.
• 1967: Intensified campaign (surveillance, containment, vaccination).
• 1977: Last natural case (Ali Maow Maalin, Somalia).
• 1980: WHO declares global eradication—only human disease so eliminated.

Key Success Factors

• Heat-stable vaccine (bifurcated needle).
• No animal reservoir; humans only host.
• Distinctive rash enabled case finding.
• Global political commitment & funding.

Legacy

• Model for polio, Guinea worm eradication efforts.
• Vaccine stockpiles maintained for bioterrorism preparedness.
• Only two WHO-sanctioned repositories remain (CDC Atlanta, VECTOR Novosibirsk).