vaccinia

virus

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 22, 2026

Quick Summary

The term "vaccinia" can refer to a poxvirus, specifically Orthopoxvirus vaccinia, which is closely related to the viruses that cause smallpox and cowpox. It also refers to a strain of this virus used in vaccines against smallpox. Historically, the word vaccinia was sometimes used interchangeably with cowpox, referring to the human form of the disease or the virus causing it.12

The vaccinia virus is a type of poxvirus, belonging to the family Poxviridae. Poxviruses are large, brick-shaped viruses containing DNA and developing within the host cell's cytoplasm. While the vaccinia virus used in modern vaccines is descended from cowpox, it has genetic differences. The development of the smallpox vaccine, initially using cowpox material, led to the eradication of smallpox worldwide by 1980.32

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

smallpox
History
…whether the new virus, called vaccinia, was a mutation of cowpox virus or a completely separate strain, but it remains the virus used for vaccine production to this day.
Read More
…whether the new virus, called vaccinia, was a mutation of cowpox virus or a completely separate strain, but it remains the virus used for vaccine production to this day.
Read More