just a hopsital?
a hopsital, seriously? that wont solve the roots of problem (still important though)
first it's all about FOOD and SANITARY
food is simple, just buy or stockpile them (it's not famine yet)
but sanitary means there's a need for cleanliness by NOT shitting(either by human or animals) in public road
it's actually harder to ask people to be clean, especially when their education and especially people from medieval (even in modern world in 2021 there's still people who shit in outdoor, looking a C country)
then public bathhouse at the very least and then lastly also a sewer ditch
road are also important, but it has little to do with plague though.
i think those are basic needs, do that and it improves tremendously
just my 2cent from a guy who works at making toilets lol
maybe for better food/meds distribution