The scientist credited with discovering the principles of vaccination is Edward Jenner. In 1796, Jenner conducted an experiment where he inoculated a young boy with cowpox, leading to immunity against smallpox. This groundbreaking work laid the foundations for the modern field of immunology. Jenner's discovery demonstrated the potential of vaccination, leading to the eventual eradication of smallpox and inspiring vaccinations for various diseases. His contributions have saved countless lives and revolutionized public health practices worldwide.