Observation and deductive reasoning. Smallpox was a scourge during Jenner's time, but he noticed that milkmaids contracted a very mild illness similar to smallpox called "cowpox", from which they recovered easily. He postulated that a tiny bit of the cowpox serum could be injected into a well person, and the mild cowpox might protect them from the deadly smallpox. It worked.
Dr Edward Jenner's qualification is that he found a vaccination for the deadly disease smallpox.
the smallpox vaccine.
Edward Jenner
yes it did work.
he was the discoverer of small-pox vaccination
He discovered a vaccination for the smallpox
hjijhijhijhjhijjhijh hello
Edward Jenner performed the first smallpox vaccination and founded the science of immunology.
I think you mean Edward Jenner: Vaccination & antiseptics and all that....
by making a small pox vaccination
Edward Jenner
!&(^ it means 1796 in caps lock