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?

1they did not interact with many people so they were not exposed to the pathogen.

2they frequently washed their hands so they were able to wash away the pathogen.

3they were exposed to cowpox, and the substance their body produced to fight cowpox also attacked smallpox.

4they breathed the air around the cows that carried an antipathogen in it that destroyed the pathogen.