I wondered what “Vocation” meant, so I did a Google, and found assorted suggestions, but they were mainly about a religious calling.

The Free Dictionary helped a bit with:

vo·ca·tion  - 

1. A regular occupation, especially one for which a person is particularly suited or qualified.

2. An inclination, as if in response to a summons, to undertake a certain kind of work, especially a religious career; a calling.

Finally the RI Website gave me the Rotary answer : 

“Vocational Service calls on every Rotarian to work with integrity and contribute their expertise to the problems and needs of society”. There was even an invitation to learn more at https://www.rotary.org/myrotary/en/document/569   

 We all know that the vocation of several of our members is in health care, but how did Edward Jenner, an English country General Practitioner, achieve such fame and recognition?

Edward Jenner was the pioneer of smallpox vaccination and the father of immunology. He was born in Berkeley, Gloucestershire in 1749, the son of the local vicar. 

At the age of 14, he was apprenticed to a local surgeon and then trained in London. In 1772, he returned to Berkeley and spent most the rest of his career as a doctor in his native town. Jenner is well known around the world for his innovative contribution to immunisation and the ultimate eradication of smallpox. 

In 1796, he carried out his now famous experiment on eight-year-old James Phipps. Jenner inserted pus taken from a cowpox pustule and inserted it into an incision on the boy's arm. He was testing his theory, drawn from the folklore of the countryside, that milkmaids who suffered the mild disease of cowpox never contracted smallpox, one of the greatest killers of the period, particularly among children. Jenner subsequently proved that having been inoculated with cowpox Phipps was immune to smallpox.

He submitted a paper to the Royal Society in 1797 describing his experiment, but was told that his ideas were too revolutionary and that he needed more proof. Undaunted, Jenner experimented on several other children, including his own 11-month-old son. In 1798, the results were finally published and Jenner coined the word vaccine from the Latin 'vacca' for cow.

Jenner was widely ridiculed. Critics, especially the clergy, claimed it was repulsive and ungodly to innoculate someone with material from a diseased animal. A satirical cartoon of 1802 showed people who had been vaccinated sprouting cow's heads. But the obvious advantages of vaccination and the protection it provided won out, and vaccination soon became widespread. Jenner became famous and now spent much of his time researching and advising on developments in his vaccine.

Jenner carried out research in a number of other areas of medicine and was also keen on fossil collecting and horticulture. He died on 26 January 1823.

Jenner's work is widely regarded as the foundation of immunology—despite the fact that he was neither the first to suggest that infection with cowpox conferred specific immunity to smallpox nor the first to attempt cowpox inoculation for this purpose.

http://www.bbc.co.uk/history/historic_figures/jenner_edward.shtml  

Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus.  The last naturally occurring case was diagnosed in October 1977, and the World Health Organization  certified the global eradication of the disease in 1980,  making smallpox the only human disease to be eradicated.  -  Wikipedia