I can answer this!

Poland strangely enough was the least affected by the plague; the plague took only about 25% of Poland's population. There's also Milan, Italy where the population taken out was less than 15%.

This reason is because the king of Poland at the time, Casmir the Great used to concept of isolation to build more borders and fortify castles as well! This was the period of Poland's prosperity in Europe.

In Milan, Italy the case is that they quarantined much better than the rest of Italy. During the plague most of the bodies were burned (Think Ring Around the Rosie) or sent to the island of Poveglia. For those affected by the plague in Milan the rule of time; Bernabo Visconti ordered that those sick were to have the windows and doors of their houses bricked immediately. Milan was also a walled city at the time and separated the population, and did not allow any trade ships in until the plague ended.

-Nero!

SOURCES: http://history.stackexchange.com/questions/16699/why-was-poland-spared-from-the-black-death

http://www.militaryhistoryonline.com/general/articles/BlackDeath.aspx

Ireland was far from unaffected by the plague but generally less affected than most other European areas. With certain outbreaks of the plague (ones before major English or Viking interaction) the Irish people lived in clans, quite different from villages. Disease would spread less as these clans would not interact as much as you would see in most European villages and thus the spread was slowed. So in short living in smaller and more isolated communities lessened the impact of the plague, although did not stop it entirely