My population was reduced by 75%, which I think was benefited by having hospitals in as many locations with over 120k population (the Yucatan is very dense) as possible. Which was like, seven. I could have maybe done more but you really need your cabinet developing the high pop provinces because they also need 20 development for a hospital
even then, hospitals in 90% of my high density locations only seemed to change it from 80-90% population loss to 75%. My first run I had like 5.3 million population, ended at 1.03 million, and in this run I had 1 million fewer to begin with and ended at 1.03ish as well
Perfidious Castile declared war, got spanked, refused to land even after The Great Deadening, so I white peaced and have focused on consolidating the Aztecs. The largest Aztec player, Tepanecapan, is my junior in a personal union. Pretty much everything that existed prior to colonization from the Yucatan to central mesoamerica is owned by a vassal (except for a tributary who I can't make into a vassal because they made that really hard for some reason)
so even severely weakened the high unity might be why Castile hasn't tried to fuck with me again despite having 110k levies to my Whole Situation's potential 29k
anyway GOT SOME TIN CAN'T WAIT TO BUILD A REAL BOAT!!
also pro tip but I'm an idiot and I thought i needed Cities to build hospitals, you can build them in towns you just need 20 development. So if you want to try to mitigate the pestilence you need your advisors developing from 1337 on to get as many 20 dev provinces in the yucatan as you can
idk if it's really worth it though, I only managed to build 7 on my highest population locations and that just reduced the death from like 90% to 75%