The Collaborative International Dictionary of English v.0.48:

Vaccinia \Vac*cin"i*a\, n. [NL. See Vaccine.] (Med.)
   Cowpox; vaccina. See Cowpox.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vaccinia
    n 1: a local infection induced in humans by inoculation with the
         virus causing cowpox in order to confer resistance to
         smallpox; normally lasts three weeks and leaves a pitted
         scar [syn: vaccinia, vaccina, variola vaccine,
         variola vaccinia, variola vaccina]
    2: a viral disease of cattle causing a mild skin disease
       affecting the udder; formerly used to inoculate humans
       against smallpox [syn: cowpox, vaccinia]