Looking at the first relevant book I found on google books (
Bubonic Plague in Early Modern Russia : Public Health and Urban Disaster)... massive, devastating and pandemic. To quote from p14;
"The effects of the Black Death on Russia extended beyond the losses of its initial onslaught. Thenceforth, the disease became enzootic for a century or more, as outbreaks recurred at gradually lengthening intervals. Until the nineteenth century, the expanding Russian state rarely enjoyed respite from plague for a decade or more... After the violent eruptions of the 14th century, the plague rarely affected more than one region or locality, but its periodic recurrence compounded the pervasive insecurity of Russian life and sapped demographic growth, especially in urban areas."
Plague also apparently significantly led to the fall of the Golden Horde and spared Moscow from a Tartar attack, so it hit nomads too.
Huh. That actually fits with an idea I had about what sort of disease come out of each direction: the East gets entirely new/mutated ones, the West gets weird originally isolated to one island plagues, that sort of thing. My thought for the North was that it didn't get new disease so much as periodically recurring old ones, as people found plague devastated villages or nomad camps that died over the winter, zombies and skeletons wandering out shadowlands or just fair folk fucking around reintroducing disease (so much tasty despair and suffering) that mostly burned out among the general populace. The winter actually helps for that, freezing some diseases for hibernation until they get dethawed by some clueless explorer (thanks the Realm!) The shadowlands also contribute as some diseases that should be dead and gone...
aren't, and that's in addition to the fun stuff like puppeteer's plague.
*Flips through link.* Hm. You know, just looking at this and how responses to plague evolved over time (from informal practices to standardized responses and inspection and quarantine stations on the borders) I think we're overlooking the 300 pound gorilla in the room: the Realm. Not in it's power to do anything directly about plagues (though if the Immaculate Order doesn't have specialist advisers they send out for plague prevention, possibly for a substantial fee, I'll be shocked) but as a holder for institutional knowledge: what worked, why it worked, and such. Moreover, just properly understanding how diseases works does wonders for stepping up how effective prevention measures are. I highly doubt that knowledge as faded into obscurity, seeing as people tend to move heaven and earth to keep medical knowledge going (not to mention Sidereals quietly reintroducing as much of it as they possibly can in the background). Given time, that's going to trickle out into other places (assuming they don't outright steal from the Realm SOP, which history suggests they would).
Overall, I think you'd see a lot more plague prevention measures in line with later plagues then the early devastating ones, or more advanced in some ways. Not in the technology used, but in the methodology used. Even ignoring whatever knowledge they've retained from past ages they can use, they've had 600 years to test and refine methodologies in real world conditions, and plague prevention improved rather a lot in Europe over a about half that time. Said methodology probably includes things not in the standard handbook, like 'get a group to punch the disease spirits in line', because it is Creation, but other then that you could probably transfer a lot. Given that, I'd imagine plagues are usually a frontier issue, and only occasionally penetrate into more central areas when they drop funding from perceived security and/or corruption of plague prevention measures.
(Thanks for the link ES.)
Or for the English example- actually, let me quote Wikipedia here, it's not the best source but it provides a dammed good idea of how nasty the Black Death was in its opening line:
Honestly, wasn't terribly interested in England, because England is a terrible model for the North. Way to temperate (an average of -10C was an exceptionally, once a century cold year), and to small. Outside some of the coastal Threshold regions, England basically is not applicable as a comparison. They don't even have permafrost, for pities sake.
(It's probably a reasonably good model for The Isle of Voices, where the Heptagram is though. Or for isles off the northern coast of the Realm.)
No, you need places like Canada or Russia to really get a feel for the North. One of those two have rather better records about what old school plagues are like, and its not the one with maple syrup. You also probably don't want the initial or exceptionally bad plagues, but rather the more ongoing ones for gauging how plagues were fought/prevented since plague is not a new thing in Creation.
(I mean, if your an Abyssal plague maker and those kinds a mega-plagues are your goal, then yeah those are handy but more for
why those plagues were so effective, and why they got less and less effective with time. Disease is devastating is something that is well established, but answer to the questions of 'why' and 'what can be done' are rather more helpful.)