Question

When Jenner developed the first vaccine he was using the observation of milk maids who

A.After having cowpox they were immune to smallpox

B.After having chickenpox they were immune to smallpox

C.After being infected with the flu virus they were immune to smallpox

D.After developing HIV they were immune to smallpox

Answer 1

After haveing cowpox they were immune to smallpox

Answer 2

A. Jenner realized that cowpox was a much less deadly version of smallpox, and used strains of that disease in his smallpox vaccine.