After 2 years (aged 23), Jenner resigned his post in London and moved back to Berkley.
There he was mostly interested in natural history and published several monographs about hedgehogs (like our friend here) and cuckoos ("Observations on ther Natural Histroy of the Cuckoo" Phil. Trans. Roy. Soc. 78: 218-237, 1788 ).
So that's how he thought up the ideas of vaccination then...