cowpox virus

Also known as: Variolae vaccinae

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Last updated

July 23, 2026

Quick Summary

Cowpox is a mild eruptive disease found in animals, particularly cats and cows, caused by a poxvirus closely related to the smallpox virus. When transmitted to humans, cowpox produces immunity to smallpox.12

English surgeon Edward Jenner demonstrated this preventive effect in 1796, observing that milkmaids who contracted cowpox were subsequently immune to smallpox. This led to the development of the smallpox vaccine. While cattle were initially thought to be the primary source of infection, rodents are now known to be a natural reservoir for the virus. The vaccinia virus used in modern vaccines, though descended from cowpox, differs genetically and is not found in nature.1

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smallpox vaccine
…used the cowpox virus (vaccinia) to confer protection against smallpox in humans. Prior to that use, however, the principle of vaccination had been applied by Asian physicians who gave children dried crusts from the lesions of people suffering from smallpox to protect against the disease. While some developed immunity,…
Read More
…used the cowpox virus (vaccinia) to confer protection against smallpox in humans. Prior to that use, however, the principle of vaccination had been applied by Asian physicians who gave children dried crusts from the lesions of people suffering from smallpox to protect against the disease. While some developed immunity,…
Read More