pre·mu·ni·tion 
(prē′my-nĭshən)
(prē′my-nĭshən)n.
Relative immunity to severe infection by a particular pathogen as a result of a chronic low-grade infection by the same pathogen.
[French prémunition, from Latin praemūnītiō, praemūnītiōn-, fortification beforehand, from praemūnītus, past participle of praemūnīre, to fortify in advance : prae-, pre- + mūnīre, to fortify; see MUNITION.]
pre·mune (prē-myn) adj.