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vaccinia vac·cin·i·a (vāk-sĭn'ē-ə)
An infection induced in humans by inoculation with the vaccinia virus in order to confer resistance to smallpox; it is usually limited to the site of inoculation. Also called primary reaction.
mildly eruptive disease of cows that when transmitted to otherwise healthy humans produces immunity to smallpox. The cowpox virus is closely related to variola, the causative virus of smallpox. The word vaccinia is sometimes used interchangeably with cowpox to refer to the human form of the disease, sometimes to refer to the causative virus, and sometimes to refer only to the artificially induced human form of cowpox.