300-500 million people in the 20th century "Smallpox: Conquered Killer" 300-500 million people in the 20th century claimed 60 million lives 300-500 million people in the 20th century "Smallpox: Conquered Killer" "Smallpox: Conquered Killer" 300-500 million people in the 20th century "Smallpox: Conquered Killer" "Smallpox: Conquered Killer" "Smallpox: Conquered Killer" claimed 60 million lives "Smallpox: Conquered Killer" 300-500 million people in the 20th century "Smallpox: Conquered Killer" 300-500 million people in the 20th century "Smallpox: Conquered Killer" "Smallpox: Conquered Killer"