Smallpox was able to be eradicated because it’s a disease that people only get once, and which does not have an animal reservoire.<p>The smallpox vaccine was intradermal, rather than intramuscular. Resistance to inoculation was reduced because it was just a scratch, rather than an injection.<p>The elimination project concentrated its efforts on outbreaks. Dr. William H. Foege developed a “ring vaccination” strategy to target vaccination around outbreaks rather than mass vaccination.