The development of the smallpox vaccine marked a pivotal turning point in medical history. Its journey began with Edward Jenner's famous 1796 experiment, where he demonstrated that inoculation with the far milder cowpox virus (Vaccinia) provided immunity against the deadly smallpox (Variola). This was a safer alternative to the risky practice of variolation, which used actual smallpox material. The vaccine proved remarkably effective, conferring solid immunity for at least 3 to 5 years, with partial protection lasting much longer. Its widespread implementation led to a dramatic and steady decline in smallpox mortality rates throughout the 19th and 20th centuries. By building population-level immunity, the vaccine directly reduced both the frequency and severity of outbreaks. This culminated in the World Health Organization's intensified global vaccination campaign, which strategically used the vaccine to isolate and eliminate the virus, leading to smallpox being declared eradicated in 1980—a feat achieved solely through the power of this groundbreaking vaccine.