VACCINIA

noun Etymology: New Latin, from vaccinus Date: 1803 a poxvirus (species Vaccinia virus of the genus Orthopoxvirus ) that differs from but is closely related to the viruses causing smallpox and cowpox and that includes a strain of uncertain natural origin used in making vaccines against smallpox, a reaction to smallpox vaccine prepared from live ~ virus that may involve a rash, fever, headache, and body pain, ~l adjective