Game concept
Plague Resistance
The game also links it as Plague Res..
From the game's encyclopedia
The Plague Resistance lowers the Infection Rate of a Barony or County, mitigating the effects of a Plague.
The Plague Resistance can be increased through Buildings like Hospices or Burial Site (Duchy Building), Court Position Tasks performed by the Personal Physician, Decisions or events.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Plague Resistance is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The Plague Resistance lowers the Infection Rate of a Barony or County, mitigating the effects of a Plague." It is part of Plague. The game also links it as Plague Res.. Patch 1.20.1.2, from game/common/game_concepts/06_ce1_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/06_ce1_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.