Which of the following best describes Jenner's achievement?

• A. Discovery of the smallpox vaccine
• B. Invention of the microscope
• C. Development of antibiotics
• D. Founding of modern surgery

Answer: (A)

Vaccination as a preventive approach to disease: Jenner demonstrated that material from cowpox could protect against smallpox, creating the first successful vaccine and establishing inoculation to build immunity. He observed that dairy workers with cowpox rarely contracted smallpox, hypothesized that exposure to one disease could confer protection against another, and tested this by inoculating a healthy boy with cowpox material. After recovery, the boy was exposed to smallpox and did not fall ill, showing that immunity had been produced. This work launched the science of immunology and the practice of vaccination, a serious turning point in public health. It is distinct from the invention of the microscope, the development of antibiotics, or the founding of modern surgery.