What does the smallpox vaccine have to do with cows?

Answer 1

The smallpox vaccine was developed by Edward Jenner, an English physician. He noticed that dairywomen who had caught cowpox - a related disease - did not catch smallpox. So he inoculated people with weakened cowpox, their bodies built up the antibodies to cowpox which then also protected them against smallpox.

Cowpox is known as Variolae Vaccinae (vacca = cow in Latin) and hence the name.

Answer 2

The word "vaccine" itself comes from a Latin word meaning "from or about cows", and the first smallpox vaccine was made from a different virus that caused a disease known as "cowpox"; the virus itself was given the name "Vaccinia" (the official name for the smallpox virus is Variola, which comes from a Latin word meaning "spotted").