How did widespread vaccination lead to the eradication of smallpox?

The eradication of smallpox was a landmark achievement in public health, made possible by the development of a safe vaccine and unprecedented global cooperation.12

In 1796, Edward Jenner discovered that infection with the cowpox virus provided cross-immunity against smallpox, a much safer alternative to earlier inoculation methods. Because smallpox had no animal reservoir and was easily identified by its characteristic rash, it was uniquely susceptible to containment.12

In 1967, the World Health Organization launched an intensified global campaign to eliminate the disease. A critical strategy was "ring vaccination," where health workers identified infected individuals, isolated them, and vaccinated all their close contacts to create a protective barrier of immune people. This approach successfully interrupted chains of transmission worldwide. Following the last recorded endemic case in 1977, the disease was officially declared eradicated in 1980, remaining the only human infectious disease to be eliminated through such efforts.312