Rubulavirus
If not vaccinated against mumps, susceptible individuals catch the disease by breathing around an infected person who has coughed or sneezed, releasing their contaminated saliva. Those who have had mumps are usually immune to future infections of the disease. Children have the highest risk of catching mumps, and it is rare for an adult to contract mumps. The incubation period for mumps can range from a couple weeks to a month, while the illness period is a few weeks. The swelling of the salivary glands is caused when the virus travels from the respiratory tract to the salivary glands and multiplies within the glands, causing the glands to swell.
Edward Jenner
Noting the common observation that milkmaids were generally immune to smallpox, Jenner postulated that the pus in the blisters that milkmaids received from cowpox (a disease similar to smallpox, but much less virulent) protected them from smallpox.
On 14 May 1796, Jenner tested his hypothesis by inoculating James Phipps, an eight-year-old boy who was the son of Jenner's gardener. He scraped pus from cowpox blisters on the hands of Sarah Nelmes, a milkmaid who had caught cowpox from a cow called Blossom, whose hide now hangs on the wall of the St George's medical school library (now in Tooting). Phipps was the 17th case described in Jenner's first paper on vaccination.