Why did vaccination replace variolation as a way to prevent smallpox?

Vaccination replaced variolation because it provided immunity to smallpox with significantly fewer risks.12

While variolation—the practice of intentionally infecting a healthy person with material from a mild case of smallpox—could provide protection, it was inherently dangerous. Recipients could develop a full-blown, potentially fatal case of the disease, and because they were infectious, they could inadvertently spread smallpox to others, acting as a new focus of infection.13

In 1796, English physician Edward Jenner demonstrated that infection with cowpox, a much milder disease, provided cross-immunity to smallpox. Because cowpox and smallpox share common antigens, vaccination allowed individuals to acquire protection without the risk of contracting or spreading smallpox. This discovery established the foundation for modern immunization, eventually leading to the global eradication of smallpox in 1980.123