Smallpox is a virus that causes a rash that then turns into painful blisters. The last known case of smallpox was in 1977. What is the best explanation for the eradication of smallpox?

The best explanation for the eradication of small pox is that the disease was eradicated due to a massive global immunization campaign led by the World Health Organization. The last known case was in Somalia in 1977. Since then, the only known cases were caused by a laboratory accident in 1978 in Birmingham, England which unfortunately killed one person. It caused a limited outbreak. After the global immunization program by the World Health Organization, small pox was declared eradicated in 1980.