Edward Jenner discovered vaccinations. He found that some of the dairymaids who worked with cows had suffered lesions
on their hands, and that these dairymaids were immune to the more severe smallpox. Which best explains why the
dairymaids were immune to smallpox?
They did not interact with many people so they were not exposed to the pathogen.
They frequently washed their hands so they were able to wash away the pathogen.
They were exposed to cowpox, and the substance their body produced to fight cowpox also attacked smallpox.
They breathed the air around the cows that carried an antipathogen in it that destroyed the pathogen.