What was the first infectious disease that was successfully prevented by a vaccine?

The first infectious disease that was successfully prevented by a vaccine is smallpox. The development of the smallpox vaccine is attributed to Edward Jenner in 1796, when he observed that milkmaids who had contracted cowpox did not become infected with smallpox. Jenner took fluid from a cowpox sore and inoculated it into a healthy person, which resulted in protection against smallpox. This groundbreaking discovery laid the foundation for the field of immunology and the development of vaccines.

Smallpox was one of the most devastating diseases in human history, and through widespread vaccination efforts, it was declared eradicated in 1980 by the World Health Organization. The success of the smallpox vaccine demonstrated the effectiveness of vaccination as a public health tool in preventing infectious diseases. Other diseases, such as measles, polio, and tuberculosis, had vaccines developed later in history, making smallpox the first disease for which a vaccine was successfully utilized to provide immunity.