Hey there! While there's always more to be said about the topic, /u/Mikedash recently wrote a fantastic series on this particular topic. I'd recommend giving it a read!

There are a few factors as to why Poland was less damaged by the Plague than the rest of Europe. Firstly, the Black Death was an urban phenomena that targeted cities first and rural developments second. Poland's infrastructure wasn't as well established at the time so while the Plague did affect them, it was usually naturally contained. Another reason is Poland's lack of trade routes at the time. The are that the Plague avoided was land locked and lacked major rivers. This made trade exclusively land based which meant there was very little outside contact. On top of the difficulties of trade, there is also no necessity for trade. Poland was the breadbasket of Europe. This means that the area was able to sustain itself and not be forced to rely on imports such as Italian city-states. There is also a cultural reason. In the East, the Mongol Kingdom, the Golden Horde, was a major enemy of all Eastern European nation, including Poland. This meant that trade routes from Moscow or other major Eastern cities along the Silk Road were blocked off. The last reason is Poland's acceptance of it's Jewish population. Western nation like France, England, Spain, etc. all had a habit of expelling their local Jewish populations. For the most part they would either flee to Amsterdam, London, Turkey, or Poland. With the influx of Jews also came the influx of their ideas. One of the Jewish ideas that may have had an effect on the Plague is their cleanliness. Jewish holy law had strict rules on cleanliness on food and on the body. It's a fact that even basic hygiene can play a huge part in fending off even the most sinister of diseases.

I got basically all of my info form this paper I found online a while back. I constantly site this as an easy to read and informative source: https://rucore.libraries.rutgers.edu/rutgers-lib/47644/PDF/1/