“The basis for vaccination began in 1796 when an English physician, Edward Jenner, observed that milkmaids previously infected with cowpox showed no symptoms of smallpox after being exposed to the virus by intentional variolation. Jenner published his treatise in 1801, “On the Origin of the Vaccine Inoculation.” In the following years, the virus used to make the smallpox vaccine changed from cowpox to vaccinia smallpox virus.5”
Ahh, is that why the etymology of vaccine involves cow?
Yes, from NIH article:
“The basis for vaccination began in 1796 when an English physician, Edward Jenner, observed that milkmaids previously infected with cowpox showed no symptoms of smallpox after being exposed to the virus by intentional variolation. Jenner published his treatise in 1801, “On the Origin of the Vaccine Inoculation.” In the following years, the virus used to make the smallpox vaccine changed from cowpox to vaccinia smallpox virus.5”