In 1796 Sarah Nelmes contracted cowpox while milking cows on her father's farm. Jenner transferred material from a cowpox pustule on Nelmes' hand to Phipps.
As related by Jenner, "On the seventh day he complained of uneasiness in the axilla, and on the ninth he became a little chilly, lost his appetite, and had a slight head-ache....." but on the 10th day he was perfectly well.... In order to ascertain whether the boy, after feeling so slight an affection of the system from Cow-pox virus, was secure from the contagion of the Small-pox, he was inoculated the 1st of July following with variolous matter (Small-pox matter, ed.) immediately taken from a pustule......No disease followed.... Several months afterwards, he was again inoculated with variolous matter, but no sensible effect was produced on the constitution."
Over the next twenty years Phipps was inoculated repeatedly for small-pox to demonstrate his permanent immunity to the disease. During this time he was employed as an assistant gardener to Jenner but got tubercles in the lungs. It was said "He was recently inoculated for small-pox, I believe, for the twentieth time without effect. He has been very ill, but is now materially better"
Phipps recovered from tuberculosis and lived with his wife and two children until he died in 1853 aged 65.